Self-testing measuring system

ABSTRACT

The invention relates to a self-testing measuring system (SS) which may have at least three modes: an operating mode and at least two test modes. In a third test mode, a digital signal generating unit (DSO) stimulates the digital input circuit (DSI) directly by means of test signals, thereby allowing this signal string to be tested. In a second test mode, the digital signal generating unit (DSO) stimulates the analogue signal string (DR, AS) and the digital input circuit (DSI) by means of test signals, thereby allowing this signal string to be tested. In a first test mode, the digital signal generating unit (DSO) stimulates the analogue signal string (DR, AS), the measuring unit (TR) (typically an ultrasound transducer) and the digital input circuit (DSI) by means of test signals, thereby allowing this signal string to be tested and monitored for parameter compliance, in particular in respect of signal amplitudes. In the operating mode, the digital signal generating unit (DSO) stimulates the analogue signal string (DR, AS), the measuring unit (TR) (typically an ultrasound transducer) and the digital input circuit (DSI) by means of output signals, thereby allowing the signal string to be monitored for parameter compliance, in particular in respect of signal amplitudes.

The invention relates to a self-testing measuring system, in particularan ultrasound sensor measuring system for automotive use, and to amethod for operating a self-testing measuring system.

GENERAL INTRODUCTION

Within the scope of the introduction of functional safety in accordancewith ISO standard 26262 in the automotive sector, ultrasound sensorsystems must also satisfy such functional safety requirements. Theserequirements are particularly high in respect of autonomous functions,for example automatic parking. In order to better identify hiddenerrors, a self-diagnosis capability is also necessary, particularlyduring operation. One problem is that the measurement results of suchultrasound measuring systems are used for example for the autonomousparking of motor vehicles. An identification of hidden errors istherefore essential.

PRIOR ART

Document DE-A-10 2013 021 328 describes an ultrasound sensor device anda corresponding method for measuring by means of ultrasonic pulses. Fordiagnosis, in the known methods, in a first test mode pulses are sent bya control command, received, and assessed in the receiver. In the secondtest mode the pulses originating from the transmitter are transmittedvia the direct connection, received, and assessed in the receiver.

Document DE-A-10 2008 042 820 describes a sensor apparatus comprising anultrasound sensor and a function monitoring apparatus for determiningthe impedance by means of a voltage level which is determined byamplifiers, filters, and microcontrollers at the sound converter. Thisdocument, too, describes an assessment of the voltage level at acomparator, wherein a monitoring signal in respect of the voltage orimpedance is formed.

The object of the invention is to describe a self-testing measuringsystem and a method for operating same, by means of which an improvedself-testing functionality may be achieved.

SOLUTION TO THE PROBLEM

In order to solve the problem, a self-testing measuring system accordingto claims 1, 30, 33 and 36, and a method according to claims 39, 40, 41and 42 are proposed. Individual embodiments of the invention are thesubject of the dependent claims. Instead of quoting these claimsverbatim, for the sake of simplicity reference can be made to theseclaims in this regard.

During the initial self-test of the proposed measuring system (SS) orwithin the scope of customer-specific diagnosis measures, various testsfor system diagnosis may be performed:

-   1. Checking the digital signal processing    -   ADVANTAGE: stimuli and expected values of the system response of        the digital signal processing may be determined in exact        fashion.-   2. Internal signal path checking    -   (Excitation of the burst generator, use of a divided driver        current, in-coupling after the first amplifier step, assessment        in accordance with the echo evaluation).    -   ADVANTAGE: this method is quick and comprehensive.-   3. Impedance value checks of the impedance of the measuring unit    (TR), that is to say for example an ultrasound transducer (TR)    -   (Execution of a frequency sweep and assessment of the resonance        profile)    -   ADVANTAGE: The method tests the complete signal path inclusive        of the external elements. The assessment of the resonance        profile of the measuring unit (TR), that is to say the        ultrasound transducer (TR), which is the system response of the        measuring unit (TR) to the stimulus in the form of the frequency        sweep, may occur in the digital signal processing already        checked in accordance with methodology 1. The frequency sweep        itself may also be produced in the digital signal processing        already checked according to number 1 above.-   4. Comparators at the sensor controller for monitoring the external    components and the driver transistors    -   ADVANTAGE: Continuous checking of the sensor excitation also        during operation.-   5. Symmetry check by symmetry checking apparatuses also during    operation    -   ADVANTAGE: Operation-relevant disturbances to the symmetry of        the measuring unit (for example the ultrasound transmitter        system) may be identified.-   6. Harmonics checking also during operation    -   ADVANTAGE: operationally relevant, non-symmetry-impairing, yet        vibration spectrum-changing disturbances to the measuring unit        (for example the ultrasound transducer/transmitter interference        subsystem) may be identified.

Checking of the Digital Signal Processing

The digital signal processing is checked by feeding at least one testsignal corresponding to a critical possible signal of the relevantmeasuring unit, for example an ultrasound sensor system in the form forexample of an ultrasound transducer. This feed is provided in the signalpath of the ultrasound sensor system in a third test mode of the sensorsystem after the analogue-to-digital converter (ADC) or in a second testmode of the sensor system before the analogue-to-digital converter(ADC). There is then an assessment of the form, as would occur in normaloperation for an actual ultrasound echo signal or measurement signal ofa measuring unit. Since both the test signal and the expected resultthereof are already known, the signal path may be checked very quicklyduring operation for continuity and functionality. This may occur duringoperation without any detriment to performance, for example atnon-operational times, or during the starting or re-starting of thesystem, or during shutdown. A feed into the signal path before theanalogue-to-digital converter (ADC) is provided here analogously via ananalogue multiplexer (AMX). A feed into the signal path after theanalogue-to-digital converter (ADC) is provided here digitally, forexample via a digital multiplexer (DMX). In the case of a digital feed,the response of the system at the end of the signal path must complyexactly with the specifications, whereas in the case of a feed in theform of analogue signal, a tolerance range must be specified or theanalogue signals should be produced with such an allowance that anincorrect assessment under consideration of the process fluctuations andthe operating parameter fluctuations is ruled out. The advantage of thismethod according to the invention is that it is particularly quick andexact.

During normal operation of the ultrasound sensor system, a rather highfunctional test coverage may hereby be maintained. These principles,however, may be generalised to similar measuring systems in which othermeasuring units may be used in accordance with the invention.

Principle:

The principle of the self-testing method proposed here comprises feedingof a test signal after or before the analogue-to-digital converter (ADC)in the analogue input circuit (AS) and assessment in accordance with theecho assessment in the subsequent digital input circuit (DSI). Checkpossible here to pass through various paths in the analogue inputcircuit (AS) and in the subsequent digital input circuit (DSI), in orderto adapt the checks as precisely as possible to the particularapplication of the measuring system (SS).

The excitation with a defined input signal by a digital input circuit(DSI) with bypassing of the non-digital signal path components leads tofixed, reproducible echo information (for example in respect of momentin time, echo level, correlation with an expected, exactly pre-knownsignal profile, etc.) at the output of the signal string in the digitalinput circuit (DSI).

This predictability is used in the invention for a self-test with oneoperating mode and three test modes of the measuring system.

A self-testing measuring system (SS) is therefore proposed, having

-   -   a digital signal generating unit (DSO) for generating the        stimuli,    -   a driver stage (DR) for power amplification and analogue signal        shaping of the digitally present stimuli,    -   a measuring unit (TR), for example an ultrasound transducer, for        converting the power-amplified stimuli into measurement signals        in the measurement medium (for example air in the case of        ultrasound) and for receiving the channel response from the        measuring channel (CH) in the form of a received signal,    -   an analogue input circuit (AS) for amplifying, pre-processing        and digitising the received signal, and    -   a digital input circuit (DSI) for processing the digitised        received signal. These components of a measuring system may be        found in the prior art in typical ultrasound measuring systems,        for example for use in automotive parking aid systems.

The previously described measuring system, on which the invention isbased, in generalised terms thus has a measuring unit which transmits anexcitation or output signal as measurement signal into a measuringchannel or a measuring section and receives a response signal in return.The measuring unit, quite generally, in this regard has at least oneactuator and at least one sensor, which are operatively connected viathe measuring channel or the measuring section. The measuring system hasan excitation (or also outward) signal path and a response (or alsoreturn) signal path. Both signal paths are provided with a digitalcircuit part and an analogue circuit part for the purpose of digitalsignal processing. The digital excitation signal is converted in theoutward signal path into an analogue excitation signal, by means ofwhich the measuring unit is controlled. It delivers over the returnedsignal path an analogue response signal, which is converted into adigital signal. The digital signal is evaluated in the measuring system,or this may also be implemented outside the measuring system. Here, itis checked whether the digital excitation signal has led to the expectedresponse signal. An analogue channel simulation unit is connectedbetween the analogue circuits in the outward and return signal path andthe measuring unit, and is connected to the outward signal path (oroptionally is connectable thereto), more specifically between theanalogue circuit and the measuring unit, and via a multiplexer orsimilar switchover unit optionally feeds its output signal, instead ofthe response signal originating from the measuring unit, into theanalogue circuit of the return signal path. A digital channel simulationunit, which is connected to the outward signal path (or optionally isconnectable thereto), is also situated between the digital circuits andthe analogue circuits of both signal paths, more specifically betweenthe digital circuit and analogue circuit thereof, and via a furthermultiplexer or similar switchover unit optionally feeds its digitaloutput signal, instead of the response signal originating from theanalogue circuit of the return signal path, into the digital circuit ofthe return signal path. The analogue channel simulation unit emulates orsimulates the measuring unit (optionally with measuring channel),whereas the digital channel simulation unit simulates the analoguecircuits of both signal paths and the measuring unit. As soon as theanalogue channel simulation unit is activated, the digital channelsimulation unit is inactive (i.e. does not feed any signal into thereturn signal path). If the digital channel simulation unit isactivated, the analogue channel simulation unit should be deactivated.Alternatively, however, in this case the analogue channel simulationunit may likewise be activated. Depending on this, different tests maybe carried out in order to examine the components of the systemaccording to the invention.

The analogue channel simulation unit may be formed as a damping memberwhich adapts the comparatively high signal level for controlling themeasuring unit (the measurement signal, in particular in the case of anultrasound measuring unit, should be energy-rich in order to cover anaccordingly large detection range) to the signal level of the responseof the measuring system. Conversely, the analogue channel simulationunit may also have an amplification signal if the ratios of the levelvalues of the control and response signals of the measuring unit areinverse as compared to that stated above. The digital channel simulationunit, in addition to the above, also emulates the functions of theanalogue circuits of both signal paths, which for example are formed inthe outward signal path as a digital-analogue converter, optionally withsignal amplification, and in the return signal path for example as ananalogue-digital converter.

In order to now enable an efficient self-test of the measuring system(SS) it is thus proposed to provide the self-testing measuring systemadditionally with an analogue channel simulation unit (ACS). Thisanalogue channel simulation unit (ACS) should be able to emulate thestring from measuring unit (TR) (or ultrasound transducer (TR)) andmeasuring channel (CN) in signal form. In order to enable this, thereturn signal path must be separated by an analogue multiplexer (AMX)before the analogue input circuit (AS), so as to optionally feed theoutput signal of the analogue channel simulation unit (ACS) there andthe output signal of the measuring unit (TR) (or the ultrasoundtransducer (TR)). It is of course also conceivable to feed the outputsignal of the analogue channel simulation unit (ACS) within the analogueinput circuit (AS) by a corresponding multiplexer structure within theanalogue input circuit (AS) or to implement elements of the analoguechannel simulation within the driver stage (DR) (i.e. the analoguecircuit of the outward signal path), which acts here also as adigital-to-analogue converter. For example, it is conceivable that thedriver stage (DR) in a test configuration is reduced in respect of itsstarting amplitude, and the analogue input circuit (AS) is controlleddirectly from the output of the driver stage (TR). The configuration ofthe driver stage (DR) is preferably controlled by a control device(CTR). The damping for example, realised by the analogue channelsimulation unit, is then used to produce a level close to operation atthe input of the analogue input circuit (AS). Critical, allowed andincorrect test cases may thus be simulated. The response of themeasuring system (SS) must lie within a predetermined expectation valuerange. Error cases and allowed operating modes may be emulated as testcases. The signal string may thus be examined, with exclusion of themeasuring channel (CN) and the measuring unit (TR) (for example anultrasound transducer) preceding and following this measuring channel(CN), for compliance with predefined specification ranges for importantoperating parameters and operating cases.

Correspondingly, a digital channel simulation unit (DCS) with a digitalmultiplexer (DMX) may be provided. The digital channel simulation unit(DCS) preferably emulates, in a manner which may be reproduced exactly,a predetermined behaviour of the signal string from driver stage (DR),measuring unit (TR), measuring channel (CN), and analogue input circuit(AS) in signal form. Critical allowed and defective operating cases maythus be simulated as check cases and test cases. The signal string maythus be checked, with exclusion of the measuring channel (CN) and themeasuring unit (TR) (for example an ultrasound transducer) preceding andfollowing the measuring channel (CN) and also the analogue circuitparts, for exact compliance of predefined specification values forimportant operating parameters and operating cases.

Thus, a plurality of (preferably four) modes of the proposed sensorsystem (SS) may thus be distinguished:

-   1. Firstly, the proposed measuring system (SS) has a mode referred    to hereinafter as the “operating mode” corresponding to the    measuring, normal operation.-   2. Secondly, the measuring system (SS) has a mode referred to    hereinafter as the “first test mode”, in which the measuring unit    (TR), for example an ultrasound transducer, is checked for correct    function. This may be implemented for example by way of an impedance    measurement of the exemplary ultrasound transducer (TR).-   3. Thirdly, the measuring system (SS) has a mode referred to    hereinafter as the “second test mode”, in which the measuring unit    (TR) itself is no longer part of the signal path. Rather, the    measuring unit (TR) and therefore also the measuring channel (CN) is    bridged by an analogue channel simulation unit (ACS) and an analogue    multiplexer (AMX). The advantage is that the behaviour of the signal    path is thus no longer dependent on the conditions in the measuring    channel (CN) or on the state of the measuring unit (TR), that is to    say for example on the state of the measuring unit (TR), for example    an ultrasound transducer (TR), and is therefore predictable.    -   If the response of the signal path in this second test mode to a        predefined stimulus does not correspond to an expected response        within certain limits, an error is thus present. Here, the        expected response must allow a certain tolerance in order to        compensate for manufacturing fluctuations which, according to        experience, are particularly pronounced in the analogue circuit        parts and the measuring unit (TR).    -   The stimulus and the stimulation of the channel may be selected        here such that both stimulus and channel response correspond to        an actual case that is allowed according to the specification.        In this case, the response of the system must therefore        correspond to an expected response within the scope of certain        limits foreseeable in advance. If this is not the case, there is        an error present.    -   The stimulus may also be selected such that it corresponds to an        actual case that is allowed according to the specification. The        simulation of the channel may then be selected here such that        the channel response corresponds to a case that is not allowed        according to the specification. In this case as well, the error        must be identified by the subsequent receive string.    -   It is of course conceivable that both the stimulus and the        simulation of the channel lead to an error case. This must also        be identified by the subsequent receive string.-   4. Fourthly, the proposed measuring system (SS) may assume a mode    referred to hereinafter as the “third test mode”, in which the    measuring unit (TR), in particular in the form of an ultrasound    transducer, and the analogue signal path components are no longer    part of the remaining signal path. The remaining signal path is then    purely digital. Responses of the remaining signal path in this third    test mode to predefined stimuli must therefore match exactly with    predefined or expected values, in contrast to the second test mode    of the measuring system (SS).    -   The stimulus and the stimulation of the channel may be selected        here such that both stimulus and channel response now correspond        exactly to an actual case that is allowed according to the        specification. In this case the response of the system must        match exactly with an associated expected response. If this is        not the case, an error is present.    -   The simulation of the channel may again also be selected such        that the channel response corresponds to an actual case that is        allowed according to specification, however the stimulus itself        should lead to an error event in the receive string. If this        error event is not identified by the digital receive string        consisting only of the digital input circuit (DSI), the digital        receive string is thus defective, which may be signalled. In        this case, the response of the system must correspond exactly to        the expected response.    -   The stimulus may also be selected here such that it corresponds        to an actual case that is allowed according to the        specification. The simulation of the channel may then be        selected here such that the channel response corresponds to a        case that is not allowed according to the specification. In this        case as well the error must be identified by the following        digital receiving string.    -   It is of course conceivable for both the stimulus and the        simulation of the channel to lead to an error case. This must        also be identified by the following digital receive string in        the third test mode.

The four modes will firstly be described hereinafter in greater detail.Further modes may be provided.

Operating Mode

In the operating mode the digital signal generating unit (DSO) generatesa first digital signal (S1), which forms or comprises said stimuli. Thedriver stage (DR) converts this first digital signal (S1) of the digitalsignal generating unit (DSO) into a second analogue signal (S2) and inso doing typically performs a digital-to-analogue conversion as well asa power amplification. The driver stage (DR), with this second analoguesignal (S2), controls the measuring unit (TR), that is to say forexample an ultrasound transducer (TR), and thus prompts this, by meansof the second analogue signal (S2), to transmit an output signal (MS)into a measuring channel (CN) in an outer region (ASOS) outside themeasuring system (SS). For example, by way of the driver stage (DR), anultrasound transducer (TR) may be prompted to transmit an output signal(MS) into an air gap as measuring channel (CN). The measuring unit (TR),that is to say for example said ultrasound transducer (TR), thenreceives a receive signal (ES) from the measuring channel (CN) atcertain times, which in the case of an ultrasound transducer (TR)preferably correspond to the times of the transmission of the ultrasoundmeasuring signal, i.e. the transmission phases (SP), depending on theoutput signal (MS). In the case of an ultrasound transducer (TR), theseare preferably echoes of the previously emitted output signal (MS),which reach the ultrasound transducer (TR) from the measuring channel(CN). The measuring unit (TR) generates a third analogue signal (S3)depending on the received receive signal (ES), which third analoguesignal is dependent on the receive signal (ES) received from themeasuring channel (CN). The exemplary ultrasound transducer (TR) forexample generates the third analogue signal (S3) depending on theultrasound receive signal (ES) that it receives from the ultrasoundmeasuring channel (CN) as an echo of the output signal (MS) emitted byitself beforehand.

The analogue multiplexer (AMX) forwards this third analogue signal (S3)as a fourth analogue signal (S4) to the analogue input circuit (AS).

The analogue input circuit (AS) converts the fourth analogue signal (S4)into a fifth digital signal (S5). It thus works on the one hand as ananalogue-to-digital converter (ADC). On the other hand, the analogueinput circuit, for example, may also comprise filters and amplifiers andother analogue circuits, which pre-process and process the receivedsignal. The digital multiplexer (DMX) forwards the fifth digital signal(S5) as sixth digital signal (S6) in the operating mode.

The digital input circuit (DSI) receives the sixth digital signal (S6)and generates a seventh response signal (S7). For example, the digitalinput circuit (DSI) may have digital filters and signal processorsystems. The use of “matched filters” (also referred to as optimalfilters), the filter function of which corresponds to expected signalforms from the previous signal string, is particularly preferred. Forexample, it is conceivable that further allowed operating configurationsare admissible that differ only by the signal path in the digital inputcircuit (DSI) and/or by the signal path in the analogue input circuit(AS) and by the associated stimuli generation in the digital signalgenerating unit (DSO) or in the configuration of the driver stage (DR).These configurations are preferably set and controlled by the (system)control device (CTR), the connection lines of which to superordinateoverall system components are not shown in the accompanying drawings.For the sake of simplicity, a single configuration of the measuringsystem (SS) has been assumed here, but is not intended to be limiting inthis respect. Since the operating mode is the normal mode, the outputsignal of the digital input circuit, that is to say the seventh responsesignal (S7), is interpreted as a signal for the measurement result andis further processed as such and/or signalled at other systemcomponents, for example a (system) control device (CTR). By contrast, inthe subsequent test modes, the seventh response signal (S7) isinterpreted and used as a test result of the measuring system (SS). Thisdoes not occur in the operating mode if the values are plausible. It isconceivable, prior to the use of the seventh response signal (S7) asmeasurement result or prior to the use of the values of the seventhresponse signal (S7) as measurement result or as measurement results, tocheck these signals or the values represented by them for plausibility,also in the operating mode, and to thus identify errors during runningoperation.

First test mode (testing of the measuring system as a whole)

In the first test mode the digital signal generating unit (DSO)generates a first digital signal (S1). This comprises predeterminedstimuli, which are intended to lead to predictable reactions of thesignal string, which can thus be checked. These stimuli may includenormal operating cases, error cases, and stimuli for measurements. Forexample, it is conceivable, in the case of the ultrasound transducer,already mentioned many times, as measuring unit (TR), to excite theultrasound transducer (TR) to a vibration at a first vibration frequencyand then to change the vibration frequency predefinably up to a secondvibration frequency, preferably rising monotonically or fallingmonotonically. Such a method for changing vibration frequency isreferred to within the scope of the invention as a “sweep”.

As in the operating mode, the driver stage (DR) converts this firstdigital signal (S1) of the digital signal generating unit (DSO) into asecond analogue signal (S2), which controls the measuring unit (TR).This second analogue signal (S2) then prompts the measuring unit (TR),that is to say for example the said ultrasound transducer (TR), totransmit an output signal (MS), that is to say for example an ultrasoundmeasurement signal, into a measuring channel (CN), that is to say forexample an ultrasound measuring channel, in an outer region (ISS)outside the measuring system (SS). As before in the operating mode, themeasuring unit (TR), that is to say for example the ultrasoundtransducer (TR), receives a receive signal (ES) from the measuringchannel (CN) depending on the previously transmitted output signal (MS).The received receive signal (ES) may be an ultrasound echo, for example.The measuring unit (TR), for example the ultrasound transducer (TR),generates a third analogue signal (S3), as before depending on thereceived receive signal (ES). The analogue multiplexer (AMX) in thisfirst test mode, as before in the operating mode, forwards this thirdanalogue signal (S3) as fourth analogue signal (S4). The analogue inputcircuit (AS) converts the fourth analogue signal (S4) into a fifthdigital signal (S5). However, in contrast to the operating mode, thesemay now also be constituted by measurement values. For example, it isconceivable to determine the impedance of an ultrasound transducer (TR),which is being used as a measuring unit (TR). This impedancedetermination occurs preferably in the analogue input circuit (AS) andoptionally in cooperation with the subsequent digital input circuit(DSI). Here, special circuit parts of the analogue input circuit (AS)and of the digital input circuit (DSI), which are only employed in thefirst test mode, may be used. In order for this to be possible, thedigital multiplexer (DMX) forwards the fifth digital signal (S5) assixth digital signal (S6). The digital input circuit (DSI) receives thesixth digital signal (S6) and generates a seventh response signal (S7).However, the seventh response signal (S7) is now used as the test resultof the measuring system and not as a measurement result. The testing forexcited harmonics and for symmetry of the control and system responsemay likewise be performed in this first test mode and will be explainedlater in greater detail.

Second test mode (testing with simulation/emulation of the measuringunit performed by the analogue channel simulation unit)

In the second test mode the digital signal generating unit (DSO) againgenerates a first digital signal (S1) as stimulus of the subsequentsignal string. The driver stage (DR) again converts this first digitalsignal (S1) of the digital signal generating unit (DSO) into a secondanalogue signal (S2), as described before. The analogue channelsimulation unit (ACS) now modifies this second analogue signal (S2) intoa third analogue test signal (S3 t). Predefined modes of the measuringchannel (CN) and of the measuring unit (TR) are preferably simulated.The analogue multiplexer (AMX) forwards this third analogue test signal(S3 t) as fourth analogue signal (S4) instead of the third analoguesignal (S3). The measuring unit (TR), that is to say for example theultrasound transducer (TR), and the measuring channel (CN) are thusbridged in defined and predetermined fashion. Since this occurs in theanalogue part of the measuring system (SS), this bridging is notperformed in in an exactly predeterminable manner, since manufacturingfluctuations and other operating parameters that cannot be influencedcompletely, such as circuit temperature, lead to behaviour fluctuationsof the signal string within the measuring system (SS), in spite of thisbridging by the analogue channel simulation unit (ACS) and the analoguemultiplexer (AMX). The analogue multiplexer (AMX) may also be configuredsuch that the analogue input circuit (AS) has two inputs, between whichit is possible to switch. In this case the analogue multiplexer (MX) isthus integrated in the analogue input circuit (AS). The invention alsoincludes this case. The behaviour of the signal string in response topredefined stimuli generated by the digital signal generating unit(DSO), however, can be examined within predefinable limits. As in theoperating mode, the analogue input circuit (AS) again converts thefourth analogue signal (S4) into a fifth digital signal (S5). Thedigital multiplexer (DMX) forwards the fifth digital signal (S5) assixth digital signal (S6) to the digital input circuit (DSI). Thedigital input circuit (DSI) receives the sixth digital signal (S6) andgenerates a seventh response signal (S7). The digital multiplexer (DMX)may also be realised in such a form that the digital input circuit (DSI)has two inputs, between which it is possible to switch. The digitalmultiplexer (DMX) is then part of the digital input circuit (DSI). Thedigital input circuit (DSI) receives the sixth digital signal (S6) andgenerates a seventh response signal (S7). As in the first test mode, theseventh response signal (S7) is now again used as test result of themeasuring system, and not as measurement result.

Third test mode (testing with simulation/emulation of the analoguecomponents of the measuring system performed by the digital channelsimulation unit (DCS))

In the third test mode the digital signal generating unit (DSO) againgenerates a first digital signal (S1) as predefined stimulus forexamining the following signal string. Now, however, the analogue partsof the signal string and the measuring unit (TR) and the measuringchannel are bridged. This bridging is performed digitally. Stimuli andthe responses of the signal string to these stimuli are therefore exactand predictable. The digital channel simulation unit (DCS) emulates thebridged parts of the signal path by preferably a plurality of emulationstates within this third test mode. To this end, the digital channelsimulation unit (DCS) preferably has a plurality of configurations,which are set and configured by the control device (CTR). The digitalchannel simulation unit (DCS) converts the first digital signal (S1)into a fifth digital test signal (S5 t). In this third test mode of themeasuring system (SS) the digital multiplexer (DMX) forwards the fifthdigital test signal (S5 t) instead of the fifth digital signal (S5) assixth digital signal (S6). The digital input circuit (DSI) receives thesixth digital signal (S6) and generates a seventh response signal (S7)corresponding to the stimulus. As in the first and second test mode, theseventh response signal (S7) is now used again as test result of themeasuring system and not as measurement result. In contrast to the firstand second test mode, however, the seventh response signal (S7) must nowsatisfy predeterminable responses exactly, since all circuit parts inthe active signal path in this third test mode of the measuring system(SS) are digital and all other parts are bridged.

Variant 1

In a further embodiment of the proposal, which preferably relates to anultrasound measuring system, a transmitter (UEB) is inserted between themeasuring unit (TR), that is to say the ultrasound transducer (TR), andthe driver stage (DR). In the example of FIG. 2, the transmitter (UEB)is connected by the third analogue signal (S3) to the measuring unit(TR), that is to say here by way of example the ultrasound transducer.In the example of FIG. 2 the third analogue signal (S3) is thusdependent both on the output signal of the transmitter (UEB) and on theinput behaviour of the measuring unit (TR), and thus in the case of anultrasound transducer is dependent on the receive signal (ES). In theoperating mode and in the first test mode, the measuring unit (TR)therefore is not prompted directly, but instead via a transmitter (UEB)by means of the second analogue signal (S2) to transmit an output signal(MS) into a measuring channel (CN) in the outer space (ASOS) outside themeasuring system (SS). The measuring unit (TR) thus generates the thirdanalogue signal (S3) depending on the received receive signal (ES) andin cooperation with the transmitter (UEB), wherein the third analoguesignal (S3) is dependent on the second analogue signal (S2) and thereceive signal (ES) received by the measuring unit (TR).

Variant 2

Variant 2 relates to a proposed measuring system (SS) corresponding tovariant 1, wherein in the operating mode at least one comparisonapparatus, in particular a comparator (C2, C3), compares a parametervalue of the third analogue signal (S3 a, S3 b) with at least onereference value (Ref2, Ref3) and generates at least one comparisonresult signal (v2, v3) depending on the comparison result. Thisparameter value may be, for example, a voltage or current level.

Variant 3

Variant 3 relates to a proposed measuring system (SS) corresponding tovariant 1, wherein in the operating mode at least one comparisonapparatus, in particular a differential amplifier (D1), compares twoparameter values of the third analogue signal (S3 a, S3 b) with oneanother, in particular by establishing a difference, and generates adifference signal (d1) and, by comparison of the difference signal (d1)with at least one reference value (Ref1), generates a comparison resultsignal (v1), in particular by means of a comparator (C1) separate fromthe comparison apparatus. These parameter values may be, for example,voltage or current levels.

Variant 4

Variant 4 relates to a proposed measuring system (SS) corresponding tovariant 1, wherein in the operating mode at least one comparisonapparatus, in particular a comparator (C4, C5, C6), compares a parametervalue of the second analogue signal (S2 a, S2 b, S2 c) with a referencevalue (Ref4, ref5, Ref6) and generates a comparison result signal (v4,v5,) depending on the comparison result. This parameter value may be,for example, a voltage or current level.

Variant 5

Variant relates to a proposed measuring system (SS) corresponding tovariant 1, wherein in the operating mode at least one comparisonapparatus, in particular a differential amplifier (D7, D6, D8), comparestwo parameter values of the second analogue signal (S2 a, S2 b, S2 c)with one another, in particular by establishing a difference, andgenerates a difference signal (d6, d7, d8) and, by comparison of thedifference signal (d6, d7, d8) with a reference value (Ref6, Ref7,Ref8), generates a comparison result signal (v10, v11, v12), inparticular by means of a comparator (C10, C11, C12) separate from thecomparison apparatus.

Variant 6

Variant 6 relates to a proposed measuring system corresponding tovariants 2, 3, 4 or 5 or the following variants, which likewise generatecomparison result signals or comparison results from a target-actualcomparison, wherein the measuring system (SS) is designed, in theoperating mode, to generate or not to generate an error messagedepending on at least one comparison result signal (v1, v2, v3, v4, v5,v6, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19).

Variant 7

Variant 7 relates to a proposed measuring system (SS) corresponding tovariant 6, wherein it comprises a control device (CTR), which assessesthe comparison result signal (v1, v2, v3, v4, v5, v6, v10, v11, v12,v13, v14, v15, v16, v17, v18, v19) and generates the error message.

Variant 8

In variant 8 the measuring unit (TR) is an ultrasound transducer (TR),which transmits an ultrasound signal measurement as output signal (MS)into an ultrasound measuring channel as measuring channel (CN) and, asreceive signal (ES), receives the ultrasound receive signal reflected atan object in the ultrasound measuring channel (CN). Alternatively, themeasuring unit (TR) may comprise at least one active element forgenerating an acoustic, optical, electric, inductive, capacitive,electromagnetic IR or UV output signal (MS) as measurement signal and atleast one sensor element for detecting a signal as receive signal inresponse to the output signal of the active element.

It is preferably provided that the measuring unit (TR) comprises anultrasound transducer, a pair formed of at least an ultrasoundtransmitter and an ultrasound receiver, a camera, in particular a TOFcamera, a pair formed of heating element and temperature sensor, a pairformed of optical transmitter and optical receiver, or at least oneother pair formed of actuator and sensor, which are operativelyconnected to one another, an anemometer, a flowmeter, a measuringbridge, a pressure and/or acceleration sensor operating on the basis ofa material deformation and having an active element for deforming thematerial for test purposes, a MEMS (micro-electrical-mechanical system),MEOS (micro-electrical-optical system), MEMOS(micro-electrical-mechanical-optical system), or the like.

Variant 9

In variant 9 the proposed measuring system (SS) comprises a controldevice (CTR) which in the first or second or third test mode comparesthe seventh response signal (S7) of the digital input circuit (DSI) witha predefined response and determines a comparison result.

Variant 10

In variant 10 the proposed measuring system (SS) comprises a controldevice (CTR) which in the first or second or third test mode controlsthe digital signal generating unit (DSO) by means of a control signal(S0) and which in the first or second or third test mode compares theseventh response signal (S7) of the digital input circuit (DSI) with apredefined response and determines a comparison result. These predefinedresponses and the control signal (S0) of the control device (CTR) aredependent on one another.

Variant 11

In variant 11 the proposed measuring system (SS) comprises a controldevice (CTR), which in the second test mode controls the analoguechannel simulation unit (ACS) such that the way in which the analoguechannel simulation unit (ACS) converts the second analogue signal (S2)into the third analogue test signal (S3 t) is dependent on this controlof the analogue channel simulation unit (ACS), and wherein the controldevice (CTR) in the second test mode compares the seventh responsesignal (S7) of the digital input circuit (DSI) with a predefinedresponse and determines a comparison result. These predefined responsesand the control of the analogue channel simulation unit (ACS) aredependent on one another.

Variant 12

In variant 12 the proposed measuring system (SS) comprises a controldevice (CTR) which in the third test mode controls the digital channelsimulation unit (DCS) such that the way in which the digital channelsimulation unit (DCS) converts the first digital signal (S1) into thefifth digital test signal (S5 t) is dependent on this control of thedigital channel simulation unit (DCS), and wherein the control device(CTR) in the third test mode compares the seventh response signal (S7)of the digital input circuit (DSI) with a predefined response anddetermines a comparison result. These predefined responses and thecontrol of the digital channel simulation unit (DCS) are dependent onone another.

Variant 13

In the thirteenth variant of the proposed measuring system (SS) thedigital input circuit (DSI) has an apparatus for measuring the vibrationfrequency of the sixth digital signal (S6) in the transmission phase(SP). This measurement of the vibration frequency enables the detectionof various kinds of damage to the resonant circuit of an ultrasoundtransducer (TR) when this is used as measuring unit (TR).

Variant 14

In the fourteenth variant of the proposed measuring system (SS) thedigital input circuit (DSI) has an apparatus for measuring the decaytime of the sixth digital signal (S6) in the decay phase (AP). Thismeasurement of the decay time enables the detection of various kinds ofdamage to the resonant circuit of an ultrasound transducer (TR) whenthis is used as measuring unit (TR). For the measurement of the decaytime, an envelope signal from the signal level profile of the thirdanalogue signal (S3) or the value profile of the sixth digital signal(S6) is preferably formed in the analogue input circuit (AS) or thedigital input circuit. If this envelope signal in the decay phase (AP)undershoots a reference value for the value of this envelope signal, thedecay of the measuring unit (TR) or of the ultrasound transducer (TR)can thus be declared as complete. Typically, the decay phase (AP) thenalso finishes. The time between the end of the transmission phase (SP)and the end, thus defined, of the decay is then the decay time.

Variant 15

In the fifteenth variant of the proposed measuring system (SS), which isbased on the thirteenth and fourteenth variants, the digital inputcircuit (DSI) or a control device (CTR) compares the measured vibrationfrequency with a target value or a target value range for this vibrationfrequency and compares the measured decay time with a target value or atarget value range for the decay time. The relevant sub-apparatus thenconcludes, as appropriate, that there is a short circuit of themeasuring unit (TR), in particular of an “inner” ultrasound transducer(TRi), or that part of the measuring unit (TR) is not provided, inparticular there is a non-connected “inner” ultrasound transducer (TRi),or a transmitter (UEB) not connected on the secondary side to a firstsub-signal (S3 a) of the third analogue signal (S3), or another generalerror. This occurs if the determined vibration frequency is higher thanthe target value of the vibration frequency or has a value above thetarget value range of the vibration frequency and if the determineddecay time is shorter than the target value of the decay time or has avalue below the target value range of the decay time. The digital inputcircuit (DSI) or the control device (CTR) then generate an errormessage.

Variant 16

In the sixteenth variant of the proposed measuring system (SS), which isbased on the thirteenth and fourteenth variants, the digital inputcircuit (DSI) or the control device (CTR) compares the measured decaytime with a target value or a target value range for this decay time andconcludes, as appropriate, that there is part of the measuring unit (TR)not provided, in particular that there is a non-connected “inner”ultrasound transducer (TRi), or that there is an error. This occurs ifthe determined decay time is shorter than the target value of the decaytime or has a value below the target value range of the decay time. Inthis case, the digital input circuit (DSI) or a control device (CTR)generates an error message.

Variant 17

In the seventeenth variant of the proposed measuring system (SS) themeasuring system (SS) has an apparatus for determining the amplitudevalue of a straight signal component (A2 c_b) in a second signal (S2) ora sub-signal (S2 c) of the second signal (S2) and has an apparatus fordetermining the amplitude value of a non-straight signal component (A2c_a) in a second signal (S2) or a sub-signal (S2 c) of the second signal(S2).

A comparison apparatus (arctan, C18), which is part of the measuringsystem (SS), is provided to compare the amplitude value (s3 b) of thestraight signal component with a threshold value (A2 c_b) for thisstraight amplitude value (s3 b) and to generate a correspondingcomparison result signal (v18) for the straight signal component (s3 b).

A further comparison apparatus, which is part of the measuring system(SS), is provided to compare the amplitude value (s3 a) of thenon-straight signal component (A2 c_a) with a threshold value for thisnon-straight amplitude value and to generate a corresponding comparisonresult signal for the non-straight signal component. A sub-apparatus ofthe measuring system (SS) then generates an error message or outputs anerror signal if the corresponding comparison result signal for thenon-straight signal component and the corresponding comparison resultsignal for the straight signal component do not correspond to an allowedvalue combination.

The terms “straight signal component” and “non-straight signalcomponent” will be defined hereinafter on the basis of the profile ofthe third sub-signal (S2 c). The profile of the third sub-signal (S2 c)is shown by way of example in FIG. 51. The third sub-signal (S2 c) has abasic frequency and an associated phase position. A “straight signalcomponent” of the sub-signal (S2 c) has the same basic frequency and thesame phase position as the sub-signal (S2 c). A “non-straight signalcomponent” of the sub-signal (S2 c) by contrast has the same basicfrequency and a phase position shifted through 90° as compared to thesub-signal (S2 c). If, for example, the sub-signal (S2 c) has acosinusoidal profile, a “straight signal part” of this sub-signal (S2 c)thus also has a cosinusoidal profile, whereas a “non-straight signalcomponent” has a sinusoidal profile.

Variant 18

In the eighteenth variant of the proposed measuring system (SS) thesecond analogue signal (S2) comprises at least one first sub-signal (S2a) and at least one second sub-signal (S2 b). The measuring system (SS)is formed by a symmetrisation of the measuring unit (TR) or of theultrasound transducer (TR) and, as applicable, of the providedtransmitter (UEB), such that the first sub-signal (S2 a) of the secondanalogue signal (S2) and the second sub-signal (S2 b) of the secondanalogue signal (S2), in the error-free case, are identical in respectof the temporal profile apart from a phase shift of 180°. The phaseshift may deviate from 180° by up to ±10°. Smaller deviations, however,are preferred. The measuring system in this eighteenth variant comprisesa sub-apparatus which is provided to measure the similarity of the firstsub-signal (S2 a) of the second analogue signal (S2) and the secondsub-signal (S2 b) of the second analogue signal (S2) and to determine ameasured value for this similarity. A phase compensation is carried outprior to the comparison. To this end, one of the two signals ispreferably delayed through 180° by suitable buffering in the controldevice (C_(TR)) or the digital input circuit (DSI). It is now proposedin this variant that the measuring system (SS) comprises a comparisondevice which compares this measured value for the similarity with areference value and generates an error signal if the value, thusdetermined, of the similarity lies below the reference value for thissimilarity. This measuring method of this eighteenth variant has theadvantage that the smallest disturbances to the symmetry of anultrasound transducer circuits may be identified.

Variant 19

In the nineteenth variant of the proposed measuring system (SS) themeasuring system (SS) may be configured such that in the first test modethe value of the impedance of the measuring unit (TR) or of theimpedance of an inner ultrasound transducer (TRi), which is part of theultrasound transducer (TR) as measuring unit, may be determined. Thisimpedance value is preferably determined in the analogue input circuit(AS) or in the digital input circuit (DSI). The digital input circuit(DSI) or the system control device (CTR) compare the determinedimpedance value with an impedance target value or provides such amessage if the detected impedance value deviates from the impedancetarget value or lies outside the impedance target value range. Thisoccurs likewise preferably in the control device (CTR) or the digitalinput circuit (DSI).

Variant 20

In the twentieth variant of the proposed measuring system (SS) themeasuring system (SS) may be configured such that in the operating modethe value profile and/or the values of the seventh response signal (S7),in particular in the form of measurement results and measured values,are checked for plausibility, in particular by the comparison withtarget values and target value ranges, by the digital input circuit(DSI) and/or the control device (CTR). For example, during theconstruction of the proposed measuring system (SS), it may be taken intoconsideration that certain measured values are not physically possibleunder certain conditions. The occurrence of such measured values underthese conditions may therefore be interpreted as an indication of anerror. It may therefore be provided that the digital input circuit (DSI)and/or the control device (CTR) in this case generate or provide anerror message.

Variant 21

In the twenty-first variant of the proposed measuring system (SS) thevalue profile and/or the values of the seventh response signal (S7),which in particular may be present in the form of measurement resultsand measured values, are/is forwarded in the operating mode by thecontrol device (CTR) and/or the digital input circuit (DSI) only if theplausibility check of the value profile and/or the values of the seventhresponse signal (S7) was successful. If the plausibility check of thevalue profile and/or the values of the seventh response signal (S7) wasnot successful, an error message for example may be generated orprovided by the control device (CTR) and/or the digital input circuit(DSI).

Variant 22

In the twenty-second variant of the proposed measuring system (SS) thedigital input circuit (DSI) and/or the analogue input circuit (AS)are/is provided and designed to detect the constant component and/or theamplitude and/or the phase and/or other signal parameters of the thirdanalogue signal (S3) at different signal frequencies of the firstdigital signal (S1) generated by the digital signal generating unit(DSO) or for different temporal signal profile patterns of the firstdigital signal (S1) generated by the digital signal generating unit(DSO). It goes without saying that in this case the digital signalgenerating unit (DSO) is able to generate different signal frequenciesof the first digital signal (S1) and/or different temporal signalprofile patterns of the first digital signal (S1). Frequency sweeps,phase jump signals, and phase-modulated signals, which may be generatedby the digital signal generating unit (DSO), are particularly suitable.

Variant 23

In the twenty-third variant of the proposed measuring system (SS) asignal profile pattern of the first digital signal (S1), which isgenerated by the digital signal reducing unit (DSO), has a signalfrequency and a phase jump within its profile.

Operating Method

It is proposed to operate the above-described apparatus and possibly itsvariants, as follows:

Firstly, the third test mode is preferably assumed by the measuringsystem (SS), and at least one test case is simulated by generating acontrol signal (S0) corresponding to this test case by the controldevice (CTR), and the seventh response signal (S7) is detected by thecontrol device (CTR), and the seventh response signal (S7) is comparedwith a predefined pattern of the seventh response signal (S7). This isbased on predefined patterns of the seventh response signal (S7) whichcorrespond to the generated control signal (S0) of the control device(CTR). It is noted here that the digital signal generating unit (DSO),the digital channel simulation unit (DCS), and the digital input circuit(DSI) may be configured differently as appropriate. These configurationsare preferably also provided by the control device (CTR). The controlsignal (S0) thereof is then dependent on these used configurations,which preferably are set by the control device (CTR) by means ofcorresponding control lines (not shown in the figures), and on theparticular purpose of the test. Accordingly, the predefined pattern ofthe seventh response signal (S7) is then also dependent on the usedcontrol signal (S0), these configurations, which are preferablycontrolled by the control device (CTR), and the purpose of the test. Anerror is determined if the seventh response signal (S7) does notcorrespond exactly to the predefined pattern of the seventh responsesignal (S7). This determination is made preferably by the control device(CTR) and is signalled at a predefined point in a predefined manner. Forexample, a flag may be set by the control device (CTR) in the event ofsuch an error. The control device (CTR), for this examination, comparesthe seventh response signal (S7) with the predefined pattern for theseventh response signal (S7). This occurs preferably by bit-wiseexamination. If no further measurements are necessary, the third testmode may then be left and another test mode or, in the error-free case,the operating mode may be assumed. In the error-free case the checkingof all check cases in the third test mode particularly preferablyfollows the checking of all check cases (test cases) in the second testmode, since the digital logic of the digital part of the signal stringis then assessed to be working correctly.

The checks in the second test mode therefore preferably follow thechecks in the third test mode. However, the second test mode may also beassumed directly from the operating mode or the other test modes.

To this end, the second test mode is assumed by the measuring system(SS), and at least one test case is simulated by generation of a controlsignal (S0) corresponding to this test case by the control device (CTR)as stimulus for the subsequent signal string, and the seventh responsesignal (S7) is detected by the control device (CTR) and the seventhresponse signal (S7) is compared with a predefined pattern corridor ofthe seventh response signal (S7). In contrast to the third test mode,the reaction of the signal string, which now also comprises analoguecircuit parts (DR, AS), may no longer be predicted exactly. Thus, asignal corridor (pattern corridor) must be predefined for the allowedprofile of the allowed values of the seventh response signal (S7). Theseventh response signal (S7) may be a one-dimensional signal, but also amulti-dimensional signal. In the multi-dimensional state space, regionsmust therefore be specified for each time step or each parameter of theseventh response signal (S7) to be checked, within which regions thevalue of the seventh response signal (S7) may move. Simple toleranceintervals, which may not be departed from, are particularly preferredfor each parameter. The pattern corridor should preferably be a simplelinear “tube”. However, significantly more complex topologies are alsoconceivable for the allowed value/parameter combinations of the seventhresponse signal (S7). If a value/parameter combination of the seventhresponse signal (S7) departs from the allowed pattern corridor, thecontrol device (CTR) may determine and signal an error. This occurs ifthe seventh response signal (S7) does not lie within the predefinedpattern corridor of the seventh response signal (S7). As soon as allcheck cases (test cases) have been processed, the second test mode ispreferably left.

In the error-free case the checking of all check cases (test cases) inthe first test mode particularly preferably follows the checking of allcheck cases in the third and second test mode, since the digital logicof the digital part of the signal string and the analogue circuit partsof the signal string are then assessed to be working correctly.

The checks in the first test mode thus preferably follow the checks inthe second test mode. The first test mode, however, may also be assumeddirectly from the operating mode or the other test modes.

To this end, the first test mode is assumed by the measuring system(SS), and at least one test case is simulated by generation of a controlsignal (S0) corresponding to this test case by the control device (CTR),and the seventh response signal (S7) is detected by the control device(CTR), and the seventh response signal (S7) is compared with apredefined pattern corridor of the seventh response signal (S7). In thistest case it is particularly important that further parameters of themeasuring unit (TR) are preferably measured. In this regard, thegeneration of the control signal (S0) preferably relates to thegeneration of suitable stimuli for the measurement of the measuring unit(TR), that is to say of the ultrasound transducer (TR), and the transferof the determined measured values for the parameters of the measuringunit (TR), that is to say of the ultrasound transducer (TR), in the formof a seventh response signal (S7) to the control device (CTR). Thecontrol device (C_(TR)) preferably determines an error if the seventhresponse signal (S7) does not lie within a predefined pattern corridorof the seventh response signal (S7). For example, this is the case ifthe impedance of the exemplary ultrasound transducer does not lie withina predefined value range or if there is an asymmetry when symmetry isexpected. To this end, the control device (CTR) and/or the digital inputcircuit (DSI) typically also assess comparison result signals ofcomparison assemblies.

In the error-free case, the checking of all check cases of the third,second and first test mode is particularly preferably followed by areturn to the operating mode, since the digital logic of the digitalpart of the signal string as well as the analogue circuit parts of thesignal string and the measuring unit, that is to say for example theultrasound transducer (TR), are assessed to be working correctly. Thismay also be determined by the control device (CTR) and may be signalledas appropriate.

The checks in the third test mode are preferably thus followed by theentering of the operating mode. However, the operating mode may also beassumed directly from all test modes.

The monitoring of amplitude levels, differences of such amplitude levelswith and without phase shifts, and the monitoring of whether there is anasymmetry where symmetry is expected may also occur in the operatingmode. To this end the control device (CTR) and/or the digital inputcircuit (DSI) typically also assess comparison result signals ofcorresponding comparison assemblies, also during normal operation in theoperating mode.

In accordance with the invention a self-testing ultrasound sensor system(SS) which comprises an “inner” ultrasound transducer (TRi), atransmitter (UEB) and a transducer resistor (R_(TR)), which may be partof the “inner” ultrasound transducer (TRi), and with a transducercapacitor (C_(TR)) which may be part of the “inner” ultrasoundtransducer (TRi) is also proposed. A first sub-signal (S2 a) of thesecond analogue signal (S2) and a second sub-signal (S2 b) of the secondanalogue signal (S2) and a first sub-signal (S3 a) of the third analoguesignal (S3) and a second sub-signal (S3 b) of the third analogue signal(S3) are the electrical minimum nodes of this proposed sub-system. Thetemporal operation of the ultrasound measuring system (SS) thentypically comprises at least the transmission phase (SP). The firstsub-signal (S2 a) of the second analogue signal (S2) is connected to afirst primary-side connection of the transmitter (UEB). The secondsub-signal (S2 b) of the second analogue signal (S2) is connected to asecond primary-side connection of the transmitter (UEB). The firstsub-signal (S3 a) of the third analogue signal (S3) is connected to afirst secondary-side connection of the transmitter (UEB) and a firstconnection of the transducer resistor (R_(TR)) and to a first connectionof the transducer capacitor (C_(TR)) and to a first connection of theinner ultrasound transducer (TRi). The second sub-signal (S3 b) of thethird analogue signal (S3) is connected to a second secondary-sideconnection of the transmitter (UEB) and a second connection of thetransducer resistor (R_(TR)) and to a second connection of thetransducer capacitor (C_(TR)) and to a second connection of the innerultrasound transducer (TRi). The topology of the circuit network formedof inner ultrasound transducer (TRi) and transducer resistor (R_(TR))and transducer capacitor (C_(TR)) and transmitter (UEB) and thecharacteristic values of these components and control thereof areselected such that, with normal operation of a transmission phase (SP),the first sub-signal (S2 a) of the second analogue signal (S2)corresponds to a second sub-signal (S2 b), phase-shifted through 180°(in particular with an allowed deviation of ±10%), of the secondanalogue signal (S2) with an amplitude deviation of less than 10%, andsuch that, with normal operation of a transmission phase (SP), the firstsub-signal (S3 a) of the third analogue signal (S3) corresponds to asecond sub-signal (S2 b), phase shifted through 180° (in particular withan allowed deviation of ±10%), of the second analogue signal (S2) withan amplitude deviation of less than 10%. At least these sub-signals (S2a, S2 b, S3 a, S3 b) have a common periodicity with the period T in thetransmission phase (SP). The ultrasound sensor apparatus (SS) comprisesat least one coefficient-monitoring sub-apparatus (KUE). Thecoefficient-monitoring sub-apparatus (KUE) analyses at least onesub-signal, specifically the signal to be analysed (ZA), which isselected from the sub-signals (S2 a, S2 b, S3 a, S3 b), for distortionsand forms an associated comparison result signal (v15, v16, v17, v18,v19) (the comparison result signal v_X).

An exemplary embodiment of the coefficient-monitoring sub-apparatus (KU)comprises a first sub-apparatus (M1, s1 a, F1, s2 a, S&H_Ca) of thecoefficient-monitoring sub-apparatus (KU), which first sub-apparatusforms a scalar product in the form of a first internal coefficientsignal (s3 a) formed of a first analysis signal (A_a) and the signal tobe analysed (ZA), and a second sub-apparatus (M2, s1 b, F2, s2 b,S&H_Cb), which forms a scalar product in the form of a second internalcoefficient signal (s1 b) formed of a second analysis signal (A_b) andthe signal to be analysed (ZA). The first analysis signal (A_a) and thesecond analysis signal (A_b) are different from one another.

The ratio of the determined value of the first internal coefficientsignal (s3 a) to the determined value of the second internal coefficientsignal (s3 b) for the normal operation in the transmission phase (SP)differs from the ratio of the determined value of the first internalcoefficient signal (s3 a) to the determined value of the second internalcoefficient signal (s3 b) for the operation in at least one error casein the transmission phase (SP). The difference between the twocoefficient signals (s3 a, s3 b) is used to generate the comparisonresult signal (v_X).

Advantage of the Invention

Such an ultrasound sensor measuring system makes it possible to test thesystem efficiently and effectively during normal operation. Theadvantages, however, are not limited to this.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be explained in greater detail hereinafter on thebasis of various exemplary embodiments and with reference to thedrawings, in which:

FIG. 1 shows, in schematically simplified form, the basic structure ofthe proposed self-testing measuring system (SS);

FIG. 2 corresponds to FIG. 1, wherein a transmitter (UEB) is insertedbetween the measuring unit (TR) and driver stage (DR);

FIG. 3 corresponds to FIG. 2 with the active signal path in theoperating mode and in the first test mode marked in bold;

FIG. 4 corresponds to FIG. 2 with the active signal path in the secondtest mode marked in bold;

FIG. 5 corresponds to FIG. 2 with the active signal path in the thirdtest mode marked in bold;

FIG. 6 corresponds to FIG. 2 with the difference that the secondanalogue signal (S2) is monitored during operation by means of acomparison unit in the form of a second comparator (C2), and the thirdanalogue signal (S3) is monitored during operation by means of acomparison unit in the form of a third comparator (C3);

FIG. 7 shows schematically a possible embodiment of the transmitter(UEB) with a three-phase primary side with three primary connections (S2a, S2 b, S2 c) and two secondary connections (S3 a, S3 b) on thesecondary side and a connected ultrasound transducer (TR) on thesecondary side;

FIG. 8 corresponds to FIG. 2, with the difference that the secondanalogue signal (S2) is three-phase and the third analogue signal (S3)is two-phase, wherein the third analogue signal (S3) is monitored duringoperation by means of comparison units;

FIG. 9 corresponds to FIG. 2 with the difference that the secondanalogue signal (S2) is three-phase and is monitored during operation bymeans of comparison units in a star configuration, and the thirdanalogue signal (S3) is two-phase;

FIG. 10 corresponds to FIG. 2 with the difference that the secondanalogue signal (S2) is three-phase and is monitored during operation bymeans of comparison units in a delta configuration, and the thirdanalogue signal (S3) is two-phase;

FIG. 11 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode;

FIG. 12 corresponds to a temporal enlargement of FIG. 11 in thetransmission phase (SP);

FIG. 13 shows important signals (S2 c, S2 a, S2 b, S5) when transmittingan ultrasound burst in the operating mode, wherein a short circuit isnow present at the inner ultrasound transducer (TRi) between the firstsub-signal (S3 a) of the third analogue signal (S3) and the secondsub-signal (S3 b) of the third analogue signal (S3);

FIG. 14 corresponds to a temporal enlargement of FIG. 13 in thetransmission phase (SP);

FIG. 15 shows important signals (S2 c, S2 a. S2 b, S5) when transmittingan ultrasound burst in the operating mode, wherein the inner ultrasoundtransducer (TRi) is now not connected, that is to say the firstsub-signal (S3 a) of the third analogue signal (S3) or the secondsub-signal (S3 b) of the third analogue signal (S3) is not connected tothe ultrasound transducer (TR);

FIG. 16 corresponds to a temporal enlargement of FIG. 15 in thetransmission phase (SP);

FIG. 17 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransmitter (UEB) is now not connected on the secondary side by means ofa connection to the third sub-signal (S3 a) of the third analogue signal(S3);

FIG. 18 corresponds to a temporal enlargement of FIG. 17 in thetransmission phase (SP);

FIG. 19 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransmitter (UEB) is now not connected on the secondary side by means ofa connection to the second sub-signal (S3 b) of the third analoguesignal (S3);

FIG. 20 corresponds to a temporal enlargement of FIG. 19 in thetransmission phase (SP);

FIG. 21 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransmitter (UEB) is now not connected on the primary side by means of aconnection to the first sub-signal (S2 a) of the second analogue signal(S2);

FIG. 22 corresponds to a temporal enlargement of FIG. 21 in thetransmission phase (SP);

FIG. 23 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransmitter (UEB) is now not connected on the primary side by means of aconnection to the second sub-signal (S2 b) of the second analogue signal(S2);

FIG. 24 corresponds to a temporal enlargement of FIG. 23 in thetransmission phase (SP);

FIG. 25 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransmitter (UEB) is now not connected on the primary side by means ofits middle connection to the third sub-signal (S2 c) of the secondanalogue signal (S2);

FIG. 26 corresponds to a temporal enlargement of FIG. 25 in thetransmission phase (SP);

FIG. 27 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side two connections of the transmitter (UEB), specifically thethird sub-signal (S2 c) of the second analogue signal (S2) and firstsub-signal (S2 a) of the second analogue signal (S2), areshort-circuited;

FIG. 28 corresponds to a temporal enlargement of FIG. 27 in thetransmission phase (SP);

FIG. 29 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side two connections of the transmitter (UEB), specifically thethird sub-signal (S2 c) of the second analogue signal (S2) and secondsub-signal (S2 b) of the second analogue signal (S2), areshort-circuited;

FIG. 30 corresponds to a temporal enlargement of FIG. 29 in thetransmission phase (SP);

FIG. 31 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransducer resistor (R_(TR)) is not connected on the secondary side,that is to say either the first sub-signal (S3 a) of the third analoguesignal (S3) or the second sub-signal (S3 b) of the third analogue signal(S3) is not connected to the transducer resistor (R_(TR));

FIG. 32 corresponds to a temporal enlargement of FIG. 31 in thetransmission phase (SP);

FIG. 33 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransducer capacitor (C_(TR)) is not connected on the secondary side,that is to say either the first sub-signal (S3 a) of the third analoguesignal (S3) or the second sub-signal (S3 b) of the third analogue signal(S3) is not connected to the transducer capacitor (C_(TR));

FIG. 34 corresponds to a temporal enlargement of FIG. 33 in thetransmission phase (SP);

FIG. 35 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side there is no control of the driver for the first sub-signal(S2 a) of the second analogue signal (S2) in the driver stage (DR);

FIG. 36 corresponds to a temporal enlargement of FIG. 35 in thetransmission phase (SP);

FIG. 37 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side the driver for the first sub-signal (S2 a) of the secondanalogue signal (S2) is short-circuited to ground in the driver stage(DR);

FIG. 38 corresponds to a temporal enlargement of FIG. 37 in thetransmission phase (SP);

FIG. 39 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side there is no control of the driver for the second sub-signal(S2 b) of the second analogue signal (S2) in the driver stage (DR);

FIG. 40 corresponds to a temporal enlargement of FIG. 39 in thetransmission phase (SP);

FIG. 41 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side the driver for the second sub-signal (S2 b) of the secondanalogue signal (S2) is short-circuited to ground in the driver stage(DR);

FIG. 42 corresponds to a temporal enlargement of FIG. 41 in thetransmission phase (SP);

FIG. 43 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side there is no control of the driver for the third sub-signal(S2 c) of the second analogue signal (S2) in the driver stage;

FIG. 44 corresponds to a temporal enlargement of FIG. 43 in thetransmission phase (SP);

FIG. 45 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side the driver for the third sub-signal (S2 c) of the secondanalogue signal (S2) is short-circuited to ground in the driver stage(DR);

FIG. 46 corresponds to a temporal enlargement of FIG. 45 in thetransmission phase (SP);

FIG. 47 shows the preferred test procedure;

FIG. 48 shows the apparatus with use of a symmetry check;

FIG. 49 shows the apparatus corresponding to FIG. 48 with specificembodiment of a symmetry check for the secondary side of the transmitter(UEB);

FIG. 50 shows the apparatus corresponding to FIG. 48 with specificembodiment of a symmetry check for the primary side of the transmitter(UEB);

FIG. 51 compares, by way of example, the undisturbed third sub-signal(S2 c) of the second analogue signal (S2) (see also FIG. 11) with thedisturbed third sub-signal (S2 c) of the second analogue signal (S2)with a capacitor disconnection of the transducer capacitor (C_(TR)) (seeFIG. 34) and shows exemplary analysis signals;

FIG. 52 shows, by way of example, a possible inner structure of ananalogue coefficient-monitoring sub-apparatus (KUE);

FIG. 53 corresponds to FIG. 8, wherein the level monitorings are notshown. Instead, possible coefficient-monitoring sub-apparatuses areshown;

FIG. 54 corresponds to FIG. 52, wherein two comparators for additionalmonitoring of the two internal coefficient signals are now provided;

FIG. 55 corresponds to FIG. 54, wherein the ratio of the two internalcoefficient signals is now not monitored;

FIG. 56 corresponds to FIG. 55, wherein only an internal coefficientsignal is now monitored;

FIG. 57 corresponds to FIG. 2, with the difference that the thirdanalogue signal (S3) is split before the analogue multiplexer (AMX) byan analogue filter or an analogue amplifier (AV) into the third analoguesignal (S3) and the amplified third analogue signal (S3′).

DESCRIPTION OF THE FIGURES

FIG. 1 schematically shows, in a simplified manner, an exemplary basicstructure of the proposed self-testing measuring system (SS) on thebasis of an exemplary ultrasound sensor system. The control device (CTR)receives data and/or programs and/or commands via a data interface (I0)from other, typically higher-ranking computers. These higher-rankingcomputers may be, for example a control unit of a motor vehicle, whichcontrols and monitors the proposed measuring system (SS). The controldevice (C_(TR)) sends determined measured values, error messages andtest results from the self-test of the measuring system (SS) to thishigher-ranking computer. The control device (CTR) controls the digitalsignal generating unit (DSO) via a control signal (S0). In addition, thecontrol device (CTR) configures preferably from all other configurablesub-apparatuses of the measuring system (SS). The corresponding controllines and signals are not shown in FIG. 1 or the corresponding followingfigures, for reasons of improved clarity.

The control signal (S0) is preferably a data bus formed of a pluralityof digital signals.

Depending on the previous history and the control signal (S0), thedigital signal generating unit (DSO) generates stimuli as well asuseful, measurement and test signals for the subsequent signal pathstring formed of the subsequent sub-apparatuses of the measuring system(SS) in the signal path. It is thus proposed to design the digitalsignal generating unit (DSO) such that it can be used as a measurementsignal generator, and as a test signal generator, and as a test patterngenerator. The digital signal generating unit (DSO) generates thestimuli and useful, measurement and test signals for the followingsignal path string as first digital signal (S1). The first digitalsignal (S1) as preferably a digital data bus. It may be that in somemodes of the allowed modes of the measuring system (SS), some lines ofthe first digital signal (S1) do not show any activity, but are activein other allowed modes of the measuring system (SS).

The driver stage (DR) generates the second analogue signal (S2)depending on the first digital signal (S1). The driver stage (DR) thusperforms a conversion of the first digital signal (S1) into an analoguesecond signal (S2). The second analogue signal (S2) may consist of aplurality of second analogue sub-signals (S2 a, S2 b, S2 c). Here aswell, not all sub-signals of the second analogue signal (S2) arenecessarily active in all modes of the measuring system (SS). In theexample disclosed here, the first sub-signal (S2 a) of the secondanalogue signal (S2) is temporally phase-shifted by 180° relative to thesecond sub-signal (S2 b) of the second analogue signal (S2). This,however, is not an inversion. The third sub-signal (S2 c) of the secondanalogue signal (S2) is the sum of the first sub-signal (S2 a) and thesecond sub-signal (S2 b) of the second analogue signal (S2) in saidexample.

The conversion does not necessarily have to be only adigital-to-analogue conversion of a digital value which has beentransmitted by means of the first digital signal (S1) to the driverstage (DR). Rather, the driver stage may also comprise more complex,possibly fed-back circuits, which change their active topology dependingon the mode of the measuring system (SS) and possibly on the currenttime within a transmission/receive sequence. For example, it is possibleto divide such a transmission/receive sequence for an ultrasound sensorsystem as exemplary measuring system (SS) into three phases. In thefirst phase of the exemplary transmission sequence (ultrasoundsequence), referred to hereinafter as the transmission phase (SP), theexemplary ultrasound transducer (TR) is excited to mechanical vibrationand therefore to transmission of an ultrasound pulse as output signal(MS) in the exemplary ultrasound measuring channel (CN). In this firstphase, that is to say the transmission phase, the driver stage (DR)applies a measurement stimulus, corresponding to the ultrasoundtransmission frequency, to the ultrasound transducer (TR). The driverstage (DR) then transports energy into the ultrasound transducer (TR).

In a second, temporally subsequent phase, that is to say the decay phase(AP), the driver stage (DR) applies a measurement stimulus, which isdirected oppositely to the vibration frequency of the still vibratingultrasound transducer, to the ultrasound transducer (TR). The driverstage (DR) then removes energy from the ultrasound transducer (TR). Inthis phase the ultrasound transducer (TR) emits an output signal (MS)into the ultrasound measuring channel (CN) in the outer region (ASS)outside the measuring system (SS) with decreasing emission amplitude.There are typically one or more objects situated in the ultrasoundchannel (CN) in the outer region (ASS) outside the measuring system(SS), which objects typically generated a heavily damped, delayed anddistorted echo of the ultrasound measuring signal. This will be referredto hereinafter as the ultrasound receive signal (ES).

In the third phase of the receive phase (EP), the ultrasound transducer(TR) is not driven by the driver stage (DR). The driver stage (DR) doesnot remove any energy from the ultrasound transducer (TR), but also doesnot transport any energy into the ultrasound transducer (TR). In thisphase, that is to say the receive phase (EP), the ultrasound transducer(TR) may receive an ultrasound echo very well as receive signal(ultrasound receive signal) (ES). The ultrasound transducer (TR) is setinto vibration by the ultrasound receive signal (ES) and on account ofits piezoelectric properties generates the third analogue signal (S3).The third analogue signal (S3) may consist of a number of analoguesub-signals (S3 a, S3 b).

An analogue multiplexer (AMX) connects through the third analogue signal(S3) as fourth analogue signal (S4) in a predefined mode of themeasuring system (SS). The signal that is connected through by theanalogue multiplexer (AMX) is dependent on the mode of the measuringsystem (SS). The analogue multiplexer (AMX) is typically controlled bythe control device (C_(TR)), which preferably controls and monitors themode and the configuration of the measuring system (SS). Here as well,not all sub-signals of the fourth analogue signal (S4) are necessarilyactive in all modes of the measuring system (SS).

The analogue input circuit (AS) receives the fourth analogue signal(S4). This receipt may be dependent on the control signal (S0) and themode of the measuring system (SS) as well as further factors. The exactway in which the receipt by the analogue input circuit (AS) occurs ispreferably specified by the control device (CTR) by means ofcorresponding control signals (not shown). The receive methodology inthe analogue input circuit (AS) preferably correlates with the usedstimulus or measurement or test signal generated by the digital signalgenerating unit (DSO) and the driver stage (DR), and with theconfiguration of the measuring system (SS) preferably set by the controldevice (C_(TR)). For example, it is conceivable to adapt analoguefilters, levels, amplifications, etc. to the predefined stimuli anduseful, measurement and test signals case-specifically. This adaptationis preferably monitored by the control device (CTR). The analogue inputcircuit (AS) generates the fifth digital signal (S5) depending on thefourth analogue signal (S4). The analogue input circuit (AS) thuspreferably also has the function of an analogue-to-digital converter(ADC). The fifth digital signal (S5) may comprise a plurality of digitalsub-signals. Here as well, not all sub-signals of the fifth digitalsignal (S5) are necessarily active in all modes of the measuring system.

A digital multiplexer (DMX) conducts the fifth digital signal (S5) assixth digital signal (S6) in a predefined mode of the measuring system(SS). The signal that is connected through by the digital multiplexer(DMX) as sixth signal (S6) is again dependent on the mode of themeasuring system (SS). The digital multiplexer (DMX) is typicallycontrolled by the control device (C_(TR)), which preferably controls andmonitors the mode of the measuring system (SS) and configurationthereof. Here as well, not all sub-signals of the sixth digital signal(S6) are necessarily active in all modes of the measuring system (SS).

The digital input circuit (DSI) receives the sixth digital signal (S6)depending on the mode of the measuring system (SS). The exact way inwhich the signal is received by the digital input circuit (DSI) this ispreferably predefined by the control device (CTR) by means ofcorresponding control signals (not shown). The receive methodology inthe digital input circuit (DSI) preferably correlates with the usedstimulus or measurement or test signal generated by the digital signalgenerating unit (DSO) and the driver stage (DR) and with the selectedreceive methodology in the analogue input circuit (AS) and theconfiguration of the measuring system (SS). For example, it isconceivable to adapt digital filters, in particular matched filters, anddigital signal processing methods to the predefined stimuli and useful,measurement and test signals and to adapt the selected receivemethodology in the analogue input circuit (AS) case-specifically. Thisadaptation is preferably monitored by the control device (CTR). Thedigital input circuit (DSI) thus generates the seventh digital signal(S7), which should already comprise the measurement, test or otherresults, depending on the sixth digital signal (S6). Another results mayalso be, for example, an error message at the control device (C_(TR)).The control device (CTR), however, may also compare measurement and testresults with target values or tolerance intervals for these targetvalues and generate error messages as appropriate. The digital inputcircuit (DSI), in predetermined modes of the measuring system, thereforenot only has the function of a signal processing, but may also have thefunction of a test apparatus for the examination that the signalprocessing string of the measuring system (SS) delivers a response tostimuli of the digital signal generating unit (DSO) corresponding to apredefined value or a predefined signal sequence with the known systemconfiguration or does not deviate therefrom by more than a predefinedamount. Here as well, not all sub-signals of the seventh digital signal(7) are necessarily active in all modes of the measuring system.

In order to now be able to test the measuring system (SS), the proposedmeasuring system (SS) has two bypass paths in the signal path.

The first bypass signal path excludes the measuring unit (TR), that isto say the ultrasound transducer (TR), from the signal path. Theelectronics may thus test themselves. For this second test mode of themeasuring system (SS) (the first test mode includes the measuring unit(TR), that is to say the ultrasound transducer (TR)), the secondanalogue signal (S2) is preferably tapped directly before the measuringunit (TR), that is to say the ultrasound transducer (TR), and by meansof the analogue multiplexer (AMX) is phased into the analogue inputcircuit (AS) instead of the third analogue signal (S3). This, however,does not occur directly. There is generally an overmodulation of theinput of the analogue input circuit (AS). The second analogue signal(S2), before the feed into the analogue input circuit (AS) as fourthanalogue signal (S4), is therefore at least damped by the analoguemultiplexer (AMX) in an additionally proposed analogue channelsimulation unit (ACS). The output signal of the analogue channelsimulation unit (ACS) is the third analogue test signal (S3 t). In thesecond test mode of the measuring system (SS), the third analogue testsignal (S3 t) instead of the third analogue signal (S3) is fed by theanalogue multiplexer (AMX) as fourth analogue signal (S4) to theanalogue input circuit (AS). As analogue channel simulation unit (ACS),configurable signal model is preferably implemented as electronicanalogue circuit which may simulate important configuration cases of thesignal section over the ultrasound transducer (TR) and the ultrasoundchannel (CN). This has the advantage that the subsequent signal path,which naturally is not precisely defined, may be simulated on thisbasis, and the function of the digital and analogue circuit parts may besimulated by a simulated measuring unit (TR) or by a simulatedultrasound transducer (TR) and a simulated ultrasound measuring channel(CN) for important, predefined cases. The various cases to be simulatedare produced, inter alia, by various configurations of the analoguechannel simulation unit (ACS). For example, it is conceivable to enablevarious dampings in the analogue channel simulation unit (ACS), so as tobe able to provide various dampings in the measuring channel (CN), thatis to say the ultrasound transmission channel (CN). Different distancesfrom objects in the ultrasound transmission channel (CN) may besimulated for example by correspondingly delayed signals by means of thedigital signal generating unit (DSO). Further simulation targets are ofcourse conceivable. The exact configuration of the analogue channelsimulation unit (ACS) is preferably predefined by the control device(CTR) by means of signals (not shown) depending on the mode of themeasuring system (SS) and the intended purpose. With regard to themeasurements for tests in the second test mode of the measuring system(SS), the measurement results are associated with a specificuncertainty, since the analogue circuit parts on the one hand areprovided with manufacturing fluctuations in respect of their parametersand on the other hand are exposed to fluctuating ambient parameters, forexample an unpredictable operating temperature, which leads tofluctuations in the measurement results. Thus, in the second test mode,a target/actual comparison when assessing the signal response of themeasuring system (SS) is preferably performed always with respect to atolerance interval for characteristic values of the signal response, andnot with respect to a precise individual value.

The second bypass excludes the analogue parts of the measuring system(SS) from the signal string. The digital electronics may thus testthemselves. For this third test mode of the measuring system (SS), thefirst digital signal (S1) is preferably tapped directly before thedriver stage (DR), that is to say the digital-to-analogue converter, andby means of the digital multiplexer (DMX) is phased into the digitalinput circuit (DSI) instead of the fifth digital signal (S5). This,however, here as well does not typically occur directly. Similarly to inthe second test mode, the first digital signal (S1), before the feedinto the digital input circuit (DSI) as sixth digital signal (S6), issuitably modified by the digital multiplexer (DMX) in an additionallyproposed digital channel simulation unit (DCS). The output signal of thedigital channel simulation unit (DCS) is the fifth digital test signal(S5 t). In the third test mode of the measuring system (SS), the fifthdigital test signal (S5 t), instead of the fifth digital signal (S5), isfed as sixth digital signal (S6) to the digital input circuit (DSI) bythe digital multiplexer (DMX). Here, however, it is expresslyconceivable to copy the first digital signal (S1) in predeterminedconfigurations of the measuring system (SS) in the third test mode bylooping through the first digital signal (S1) by the digital channelsimulation unit (DCS) as fifth digital test signal (S5 t) to the sixthdigital signal (S6). In this regard, the digital channel simulation unit(DSI) may also consist only of wire bridges—i.e. of a direct connectionbetween first digital signal (S1) and fifth digital test signal (S5 t).A configurable signal model as electronic digital circuit is preferablyagain implemented as digital channel simulation unit (DCS). and maysimulate important configuration cases of the signal section that runsvia the driver stage (DR), the ultrasound transducer (TR), theultrasound channel (CH), and the analogue input circuit (AS) and theother auxiliary circuits. The exact configuration of the digital channelsimulation unit (DCS) is predefined, preferably by the control device(CTR) by means of signals (not shown), depending on the mode of themeasuring system (SS) and the intended purpose. This has the advantagethat the subsequent signal path, which naturally is not preciselydefined, again may be simulated on this basis, and the function of thedigital circuit parts may be simulated EXACTLY by a simulated ultrasoundtransducer (TR) and a simulated ultrasound measuring channel (CN) andsimulated analogue parts for important, predefined cases. The variouscases to be simulated are produced here by various configurations of thedigital channel simulation unit (DCS). For example, it is conceivable tosimulate various defective and non-defective signal responses of thesubsequent signal path and to examine the correct response of thedigital input circuit. Further simulation objectives are of courseconceivable. With regard to the measurements for tests in the third testmode of the measuring system, the measurement results are not associatedwith any uncertainty and are therefore exact. The digital circuit partsare relatively immune to said manufacturing fluctuations and saidfluctuations of ambient parameters. In the third test mode atarget/actual comparison when assessing the signal response of themeasuring system is therefore performed always with respect to precisevalues.

The digital input circuit (DSI) signals the measurement and test resultsas well as any generated error messages at the control apparatus(C_(TR)) by means of the seventh digital signal (S7), which may comprisea plurality of digital sub-signals.

FIG. 2 corresponds to FIG. 1, wherein a transmitter (UEB) has beeninserted between the measuring unit (TR), that is to say the ultrasoundmeasuring system, and the driver stage (DR). The third analogue signal(S3) in this example is removed on the secondary side of the transmitter(UEB), whereas the second analogue signal (S2) in this example isconnected on the primary side of the transmitter (UEB). In the operatingmode and in the first test mode, the cooperation of transmitter (UEB)and ultrasound transducer (TR) may be monitored and assessed by means ofthe analogue input circuit (AS) and the digital input circuit (DSI).

FIG. 3 corresponds to FIG. 2 with the signal path active in theoperating mode and in the first test mode marked in bold. The measuredvalues of the ultrasound sensor system are obtained in the operatingmode in this way, in accordance with the prior art. What is shown istherefore the signal path when the measuring system (SS) is not testingitself. This signal path is also selected in the first test mode. Inthis first test mode the ultrasound transducer (TR) is stimulatedsuitably, and the response of the ultrasound transducer (TR) ismeasured. To this end, the constant component, amplitude and phase ofthe third analogue signal (S3) for example may be analysed at differentstimulation frequencies and with different stimulation patterns. Forexample, the response to a phase jump may be detected. The detection ofthe impedance of the ultrasound transducer (TR) is particularlyadvantageous, since this is also dependent on the properties of theultrasound measuring channel. If, for example, the ultrasound transducer(TR) ices over, it's acoustic impedance thus changes, Asda is also itselectrical impedance.

FIG. 4 corresponds to FIG. 2 with the signal path active in the secondtest mode shown in bold.

FIG. 5 corresponds to FIG. 2 with the signal path active in the thirdtest mode shown in bold.

FIG. 6 corresponds to FIG. 2 with the difference that the secondanalogue signal (S2) is monitored during operation by means of acomparison unit in the form of a second comparator (C2) and the thirdanalogue signal (S3) is monitored during operation by means of acomparison unit in the form of a third comparator (C3). This monitoringmay be designed here such that the comparators (C2, C3) compare maximumvalues or minimum values or amounts with their respective referencevalues (Ref2, Ref3). The comparison of the value of the particularanalogue signal (S2, S3) with the corresponding reference value (Ref2,Ref3) is particularly preferred. If this reference value (Ref2, Ref3) isovershot, the corresponding comparison result signal (v2, v3) is thusgenerated. This comparison result signal (v2, v) may be conducted forexample directly to a superordinate unit or to a control device (CTR) orto the digital input circuit (DSI). However, assessment of the relevantcomparison result signal (v2, v3) by the control device (CTR) ispreferred. This preferably assesses the comparison result signals (v2,v3) and generates, as appropriate, suitable status messages or errormessages, which it forwards via the data interface (I0) to thesuperordinate unit (for example a control unit in a motor vehicle). Inthe example of FIG. 6 a second comparator (C2) compares the value of thelevel of the second analogue signal (S2) with a second reference value(Ref2) and generates a second comparison result signal (v2) depending onthis comparison. The polarity of the comparison result signal, which ispreferably a digital signal, is irrelevant, since this is dependent onlyon the logical meaning. For example, it is expedient in the first phaseof the transmission sequence, in which the ultrasound transducer (TR)receives energy from the driver stage (DR), to check a minimum amplitudeof the second analogue signal (S2).

The momentary value of the second analogue signal (S2) must thereforeovershoot the second reference value (Ref2). Since the second analoguesignal (S2), however, is generally a pulsed signal, this overshoot isonly expected during the pulse and therefore can only also be checked atthat time. In this regard, a suitable synchronisation of the measuredvalues must be provided. Conversely, a reference value must not beundershot at those times at which there is no pulse present over thesecond analogue signal (S2). It may therefore be expedient to provide,instead of a single second reference value (Ref2), a plurality of secondreference values, in order to be able to check the correct control ofthe ultrasound transducer (TR) or of the transmitter (UEB) by the driverstage (TR). The time control of this check may be implemented either bya separate test apparatus or for example by the digital signalgenerating unit (DSO) or the control device (CTR).

The momentary value of the third analogue signal (S3) must thereforeovershoot the third reference value (Ref3). Since the third analoguesignal (S3), however, is generally a sinusoidal vibration, thisovershoot is only expected during the maximum of the wave crests andtherefore can only also be checked at that time. The third analoguesignal (S3), however, may have an equivalent value. It is therefore alsoexpedient here to check not only the maximum of the wave crests, butalso the minima of the wave troughs. The momentary value of the thirdanalogue signal (S3) therefore must not undershoot another thirdreference value (Ref3). In this regard, it may be expedient to providetwo third comparators (C3) with two different third reference values(Ref3), in order to be able to check the correct functioning of theultrasound transducer (TR) in cooperation with the transmitter (UEB) atpredetermined times with correct phase position. The time control ofthis check may be implemented again either by a separate test apparatusor for example by the digital signal generating unit (DSO) or thecontrol device (C_(TR)).

FIG. 7 shows schematically a possible embodiment of the transmitter(UEB) with a three-phase primary side with three primary connections (S2a, S2 b, S2 c) and two secondary connections (S3 a, S3 b) on thetwo-phase secondary side and a connected ultrasound transducer (TR) onthe secondary side. The ultrasound transducer (TR) comprises, assub-components, a transducer resistor (R_(TR)), a transducer capacitor(C_(TR)), and the inner ultrasound transducer (TRi), which comprises thepiezoelectric vibration element and emits the output signal (MS) andreceived the ultrasound receive signal (ES). In this example thetransmitter (UEB) on the primary side has a symmetrical centre tap,which is connected to the third sub-signal (S2 c) of the second analoguesignal (S2). One of the other primary-side connections of thetransmitter (UEB) is connected to the first sub-signal (S2 a) of thesecond analogue signal (S2). The third primary-side connection of thetransmitter (UEB) is connected to the second sub-signal S2 b) of thesecond analogue signal (S2). On the secondary side, all components (UEB,RTR, CTR, TRi) are connected in parallel between the first sub-signal(S3 a) of the third analogue signal (S3) and the second sub-signal (S3b) of the third analogue signal (S3). This results in a resonantcircuit, the inherent vibration frequency and quality of which aredependent on the secondary-side elements and the primary-side control.The vibration properties of this resonant circuit change in the event ofshort circuits and line breaks and may be detected.

FIG. 8 corresponds to FIG. 2 with the difference that the secondanalogue signal (S2) is three-phase and the third analogue signal (S3)is two-phase with a first sub-signal (S3 a) and a second sub-signal (S3b), wherein the third analogue signal (S3) is monitored during operationby means of comparison units. In this example the third analogue testsignal (S3 t) is therefore likewise two-phase, with a first sub-signal(S3 ta) and a second sub-signal S3 tb). The analogue channel simulationunit (ACS) then generates the first sub-signal (S3 ta) of the thirdanalogue test signal (S3 t) and the second sub-signal (S3 tb) of thethird analogue test signal (S3 t) from the first sub-signal (S2 a) ofthe second analogue signal (S2) and the second sub-signal (S2 b) of thesecond analogue signal (S2) and the third sub-signal (S2 c) of thesecond analogue signal (S2) when the measuring system (SS) is in thesecond test mode. The transmitter (UEB) and ultrasound transducer (TR)should correspond here to FIG. 7 and should be connected accordingly.

A first differential amplifier (D1) forms the first difference signal(d1) for example by establishing a difference from a parameter value ofthe first sub-signal (S3 a) of the third analogue signal (S3) and from aparameter value of the second sub-signal (S3 b) of the third analoguesignal (S3). For example, this may be a simple establishment of adifference between the momentary values of the electrical potential ofthe first sub-signal (S3 a) of the third analogue signal (S3) and thesecond sub-signal (S3 b) of the third analogue signal (S3) with respectto a reference potential. In this case the first difference signal (d1)constitutes the value of the voltage difference between the momentaryvalues of the electrical reference potential of the first sub-signal (S3a) of the third analogue signal (S3) and the second sub-signal (S3 b) ofthe third analogue signal (S3) with respect to a reference potential. Inother applications, instead of comparing electrical potential valueswith respect to a preferably common reference potential, current valuesmay also be compared.

A first comparator (C1) compares the momentary value of the firstdifference signal (d1) with a first reference value (Ref1) and forms thefirst comparison result signal (v1). As before, it may be expedient todetect overshoots at certain times and to detect undershoots at othertimes within an ultrasound Transmission sequence. It may therefore beexpedient to provide a plurality of first reference values (Ref1) forthese different times and moments in time, which first reference valuesshould preferably be different. A separate first comparator (C1) mayoptionally be provided for each of these first reference values (Ref1),which comparators each generate an associated first comparison resultsignal (v1). The first comparison result signals (v1) are preferablyassessed by the control device (CTR) or the digital input circuit (DSI).The moments in time at which the first comparison result signals (v1)are valid and should be assessed are preferably defined by the digitalsignal generating unit (DSO) or the control device (CTR).

A second comparator (C2) compares the momentary value of the firstsub-signal (S3 a) of the third analogue signal (S3) with a secondreference value (Ref2) and forms the second comparison result signal(v2). As before, it may be expedient to detect overshoots at certaintimes and to detect undershoots at other times within an ultrasoundtransmission sequence. It may therefore be expedient to provide aplurality of second reference values (Ref2) for these different timesand moments in time, which second reference values should preferably bedifferent. A separate second comparator (C2) may optionally be providedfor each of these second reference values (Ref2), which comparators eachgenerate an associated second comparison result signal (v2). The secondcomparison result signals (v2) are preferably assessed by the controldevice (CTR) or the digital input circuit (DSI). The moments in time atwhich the second comparison result signals (v2) are valid and should beassessed are preferably defined by the digital signal generating unit(DSO) or the control device (CTR).

A third comparator (C3) compares the momentary value of the secondsub-signal (S3 b) of the third analogue signal (S3) with a thirdreference value (Ref3) and forms the third comparison result signal(v3). As before, it may be expedient to detect overshoots at certaintimes and to detect undershoots at other times, for example within anultrasound transmission sequence. It may therefore be expedient toprovide a plurality of third reference values (Ref3) for these differenttimes and moments in time, which third reference values shouldpreferably be different. A separate third comparator (C3) may optionallybe provided for each of these third reference values (Ref3), whichcomparators each generate an associated third comparison result signal(v3). The third comparison result signals (v3) are preferably assessedby the control device (CTR) or the digital input circuit (DSI). Themoments in time at which the third comparison result signals (v3) arevalid and should be assessed are preferably defined by the digitalsignal generating unit (DSO) or the control device (CTR).

FIG. 9 corresponds to FIG. 2, with the difference that the secondanalogue signal (S2) is three-phase and is monitored during operation bymeans of comparison units in a star configuration, and the thirdanalogue signal (S3) is two-phase.

A fourth comparator (C4) compares the momentary value of the secondsub-signal (S2 b) with a fourth reference value (Ref4) and forms thefourth comparison result signal (v4). As before, it may be expedient todetect overshoots at certain times and to detect undershoots at othertimes, for example within an ultrasound transmission sequence. It maytherefore be expedient to provide a plurality of fourth reference values(Ref4) for these different times and moments in time, which fourthreference values should preferably be different. A separate fourthcomparator (C4) may optionally be provided for each of these fourthreference values (Ref4), which comparators each generate an associatedfourth comparison result signal (v4). The fourth comparison resultsignals (v4) are preferably assessed by the control device (CTR) or thedigital input circuit (DSI). The moments in time at which the fourthcomparison result signals (v4) are valid and should be assessed arepreferably defined by the digital signal generating unit (DSO) or thecontrol device (C_(TR)).

A fifth comparator (C5) compares the momentary value of the thirdsub-signal (S2 c) of the second analogue signal (S2) with a fifthreference value (Ref5) and forms the fifth comparison result signal(v5). As before, it may be expedient to detect overshoots at certaintimes and to detect undershoots at other times, for example within anultrasound transmission sequence. It may therefore be expedient toprovide a plurality of fifth reference values (Ref5) for these differenttimes and moments in time, which fifth reference values shouldpreferably be different. A separate fifth comparator (C5) may optionallybe provided for each of these fifth reference values (Ref5), whichcomparators each generate an associated fifth comparison result signal(v5). The fifth comparison result signals (v5) are preferably assessedby the control device (CTR) or the digital input circuit (DSI). Themoments in time at which the fifth comparison result signals (v5) arevalid and should be assessed are preferably defined by the digitalsignal generating unit (DSO) or the control device (CTR).

A sixth comparator (C6) compares the momentary value of the firstsub-signal (S2 a of the second analogue signal (S2)) with a sixthreference value (Ref6) and forms the sixth comparison result signal(v6). As before, it may be expedient to detect overshoots at certaintimes and to detect undershoots at other times, for example within anultrasound transmission sequence. It may therefore be expedient toprovide a plurality of sixth reference values (Ref6) for these differenttimes and moments in time, which sixth reference values shouldpreferably be different. A separate sixth comparator (C6) may optionallybe provided for each of these sixth reference values (Ref6), whichcomparators each generate an associated sixth comparison result signal(v6). The sixth comparison result signals (v6) are preferably assessedby the control device (CTR) or the digital input circuit (DSI). Themoments in time at which the sixth comparison result signals (v6) arevalid and should be assessed are preferably defined by the digitalsignal generating unit (DSO) or the control device (CTR).

FIG. 10 corresponds to FIG. 6, with the difference that the secondanalogue signal (S2) is three-phase and is monitored during operation bymeans of comparison units in a delta configuration, and the thirdanalogue signal (S3) is two-phase.

A second differential amplifier (D2) forms the second difference signal(d2) for example by establishing a difference from a parameter value ofthe second sub-signal (S2 b) of the second analogue signal (S2) and froma parameter value of the third sub-signal (S2 c) of the second analoguesignal (S2). For example, this may be a simple establishment of adifference between the momentary values of the electrical potential ofthe second sub-signal (S2 b) of the second analogue signal (S2) and thethird sub-signal (S2 b) of the second analogue signal (S2) with respectto a reference potential. In this case the second difference signal (d2)constitutes the value of the voltage difference between the momentaryvalues of the electrical potential of the second sub-signal (S2 b) ofthe second analogue signal (S2) and the third sub-signal (S2 c) of thesecond analogue signal (S2) with respect to a reference potential. Inother applications, instead of comparing electrical potential valueswith respect to a preferably common reference potential, current valuesmay also be compared.

A tenth comparator (C10) compares the momentary value of the seconddifference signal (d2) with a seventh reference value (Ref7) and formsthe tenth comparison result signal (v10). As before, it may be expedientto detect overshoots at certain times and to detect undershoots at othertimes, for example within an ultrasound transmission sequence. It maytherefore be expedient to provide a plurality of seventh referencevalues (Ref7) for these different times and moments in time, whichseventh reference values should preferably be different. A separatetenth comparator (C10) may optionally be provided for each of theseseventh reference values (Ref7), which comparators each generate anassociated tenth comparison result signal (v10). The tenth comparisonresult signals (v10) are preferably assessed by the control device (CTR)or the digital input circuit (DSI). The moments in time at which thetenth comparison result signals (v10) are valid and should be assessedare preferably defined by the digital signal generating unit (DSO) orthe control device (CTR).

A third differential amplifier (D3) forms the third difference signal(d3) for example by establishing a difference from a parameter value ofthe third sub-signal (S2 c) of the second analogue signal (S2) and froma parameter value of the first sub-signal (S2 a) of the second analoguesignal (S2). For example, this may be a simple establishment of adifference between the momentary values of the electrical potential ofthe third sub-signal (S2 c) of the second analogue signal (S2) and thefirst sub-signal (S2 a) of the second analogue signal (S2) with respectto a reference potential. In this case the third difference signal (d3)constitutes the value of the voltage difference between the momentaryvalues of the electrical potential of the third sub-signal (S2 c) of thesecond analogue signal (S2) and the first sub-signal (S2 a) of thesecond analogue signal (S2) with respect to a reference potential. Inother applications, instead of comparing electrical potential valueswith respect to a preferably common reference potential, current valuesmay also be compared.

A eleventh comparator (C11) compares the momentary value of the thirddifference signal (d3) with an eighth reference value (Ref8) and formsthe eleventh comparison result signal (v11). As before, it may beexpedient to detect overshoots at certain times and to detectundershoots at other times, for example within an ultrasoundtransmission sequence. It may therefore be expedient to provide aplurality of eighth reference values (Ref8) for these different timesand moments in time, which eighth reference values should preferably bedifferent. A separate eleventh comparator (C11) may optionally beprovided for each of these eighth reference values (Ref8), whichcomparators each generate an associated eleventh comparison resultsignal (v11). The eleventh comparison result signals (v11) arepreferably assessed by the control device (CTR) or the digital inputcircuit (DSI). The moments in time at which the eleventh comparisonresult signals (v11) are valid and should be assessed are preferablydefined by the digital signal generating unit (DSO) or the controldevice (CTR).

A fourth differential amplifier (D4) forms the fourth difference signal(d4) for example by establishing a difference from a parameter value ofthe first sub-signal (S2 a) of the second analogue signal (S2) and froma parameter value of the second sub-signal (S2 b) of the second analoguesignal (S2). For example, this may be a simple establishment of adifference between the momentary values of the electrical potential ofthe first sub-signal (S2 a) of the second analogue signal (S2) and thesecond sub-signal (S2 b) of the second analogue signal (S2) with respectto a reference potential. In this case the fourth difference signal (d4)constitutes the value of the voltage difference between the momentaryvalues of the electrical potential of the first sub-signal (S2 a) of thesecond analogue signal (S2) and the second sub-signal (S2 b) of thesecond analogue signal (S2) with respect to a reference potential. Inother applications, instead of comparing electrical potential valueswith respect to a preferably common reference potential, current valuesmay also be compared.

A twelfth comparator (C12) compares the momentary value of the fourthdifference signal (d4) with a ninth reference value (Ref9) and forms thetwelfth comparison result signal (v12). As before, it may be expedientto detect overshoots at certain times and to detect undershoots at othertimes, for example within an ultrasound transmission sequence. It maytherefore be expedient to provide a plurality of ninth reference values(Ref9) for these different times and moments in time, which ninthreference values should preferably be different. A separate twelfthcomparator (C12) may optionally be provided for each of these ninthreference values (Ref9), which comparators each generate an associatedtwelfth comparison result signal (v12). The twelfth comparison resultsignals (v12) are preferably assessed by the control device (CTR) or thedigital input circuit (DSI). The moments in time at which the twelfthcomparison result signals (v12) are valid and should be assessed arepreferably defined by the digital signal generating unit (DSO) or thecontrol device (CTR).

FIG. 11 shows the temporal course of important signals (d1, S2 c, S2 a,S2 b, S5) during transmission of an ultrasound burst in the operatingmode. The following can be clearly seen:

-   1. the first phase of the transmission frequency, the transmission    phase (SP), in which the driver stage drives the ultrasound    transducer (TR), and an output signal (MS) is transmitted by the    ultrasound transducer; and-   2. the second phase of the transmission sequence, that is to say the    decay phase, in which the driver stage removes energy from the    ultrasound transducer (TR) and damps its mechanical vibration, and-   3. the receive phase (EP), in which the ultrasound transducer (TR)    can receive an echo of an output signal (MS).

The following are also shown:

-   1. the first difference signal (d1), which reproduces the    differential amplitude of the electrical potential difference    between the first sub-signal (S3 a) of the third analogue signal    (S3) and the second sub-signal (S3 b) of the third analogue signal    (S3), and-   2. the third sub-signal (S2 c) of the second analogue signal (S2),    which reproduces the level of the electrical potential at the centre    tap of the transmitter (UEB), and-   3. the first sub-signal (S2 a) of the second analogue signal (S2),    which reproduces the level of the electrical potential at a first    connection of the transmitter (UEB), and-   4. the second sub-signal (S2 c) of the second analogue signal (S2),    which reproduces the level of the electrical potential at a second    connection of the transmitter (UEB), and-   5. the digitised value of the fifth digital signal (S5), which    reproduces the analogue amplified, filtered and digitised value.

FIG. 12 corresponds to a temporal enlargement of FIG. 11, wherein thedetail in the transmission phase (SP) is temporally localised.

FIG. 13 shows important signals (S2 c, S2 a, S2 b, S5) when transmittingan ultrasound burst in the operating mode, wherein a short circuit isnow present at the inner ultrasound transducer (TRi) between the firstsub-signal (S3 a) of the third analogue signal (S3) and the secondsub-signal (S3 b) of the third analogue signal (S3).

Symptoms

The ultrasound transducer does not vibrate correctly. Thus, a frequencymeasurement and a measurement of the decay time may be taken by thedigital input circuit (DSI). With the proposed apparatus, the case of ashort-circuited ultrasound transducer (TR), in which the secondsub-signal (S3 b) of the third analogue signal (S3) is connected to thefirst sub-signal (S3 a) of the third analogue signal (S3), may beidentified.

FIG. 14 corresponds to a temporal enlargement of FIG. 13.

FIG. 15 shows important signals (S2 c, S2 a, S2 b, S5) when transmittingan ultrasound burst in the operating mode, wherein the inner ultrasoundtransducer (TRi) is now not connected, that is to say the firstsub-signal (S3 a) of the third analogue signal (S3) or the secondsub-signal (S3 b) of the third analogue signal (S3) is not connected tothe ultrasound transducer (TR).

Symptoms

The ultrasound transducer does not vibrate correctly. Thus, ameasurement of the decay time may be taken by the digital input circuit(DSI). With the proposed apparatus, the case of a non-connected innerultrasound transducer (TRi) may thus be identified.

FIG. 16 corresponds to a temporal enlargement of FIG. 15.

FIG. 17 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransmitter (UEB) is now not connected on the secondary side by means ofa connection to the first sub-signal (S3 a) of the third analogue signal(S3).

Symptoms

The non-connected first sub-signal (S3 a) of the third analogue signal(S3) means that the inner ultrasound transducer (TRi)is not sufficientlysupplied with energy. This error is therefore detectable by anassessment of the decay time and the vibration frequency.

FIG. 18 corresponds to a temporal enlargement of FIG. 17.

FIG. 19 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransmitter (UEB) is now not connected on the secondary side by means ofa connection to the second sub-signal (S3 b) of the third analoguesignal (S3).

Symptoms

The non-connected second sub-signal (S3 b) of the third analogue signal(S3) means that the inner ultrasound transducer (TRi) is notsufficiently supplied with energy. This error is therefore againdetectable by means of an evaluation of the decay time and the vibrationfrequency.

FIG. 20 corresponds to a temporal enlargement of FIG. 19.

FIG. 21 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransmitter (UEB) is now not connected on the primary side by means of aconnection to the first sub-signal (S2 a) of the second analogue signal(S2).

Symptoms

The non-connected first sub-signal (S2 a) of the second analogue signal(S2) means that the ultrasound transducer (TR) is not sufficientlysupplied with energy. This error, however, is not detectable by means ofan assessment of the decay time and the vibration frequency.

A sixth comparator (C6) at the first sub-signal (S2 a) of the secondanalogue signal (S2) (see also FIG. 9) may detect the continuousundershooting of this sixth reference value (Ref6) in the transmissionphase (SP) and/or in the receive phase (EP) by comparison with a sixthreference (Ref6) and may thus conclude that the transmitter (UEB) is notconnected on the secondary side by means of a connection to the firstsub-signal (S2 a) of the second analogue signal (S2). The setting of thecorresponding sixth comparison signal (v6) may be identified by the(system) control device (CTR) or the digital input circuit (DSI). Thesethen issue a corresponding error signal or a corresponding errormessage.

FIG. 22 corresponds to a temporal enlargement of FIG. 21.

FIG. 23 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransmitter (UEB) is now not connected on the primary side by means of aconnection to the second sub-signal (S2 b) of the second analogue signal(S2).

Symptoms

The non-connected second sub-signal (S2 b) of the second analogue signal(S2) means that the ultrasound transducer (TR) is not sufficientlysupplied with energy. This error, however, is not detectable by means ofan assessment of the decay time and the vibration frequency.

A fourth comparator (C4) at the second sub-signal (S2 b) of the secondanalogue signal (S2) (see also FIG. 9) may detect the continuousundershooting of this fourth reference value (Ref4) in the transmissionphase (SP) and/or in the receive phase (EP) by comparison with a fourthreference (Ref4) and may thus conclude that the transmitter (UEB) is notconnected on the secondary side by means of a connection to the secondsub-signal (S2 b) of the second analogue signal (S2). The setting of thecorresponding fourth comparison signal (v4) may be identified by the(system) control device (CTR) or the digital input circuit (DSI). Thesethen preferably issue a corresponding error signal or a correspondingerror message.

FIG. 24 corresponds to a temporal enlargement of FIG. 23.

FIG. 25 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransmitter (UEB) is not connected on the primary side by means of itsmiddle connection to the third sub-signal (S2 c) of the second analoguesignal (S2).

Symptoms

The non-connected third sub-signal (S2 c) of the second analogue signal(S2) means that the inner ultrasound transducer (TRi)is not sufficientlysupplied with energy. This error is detectable by an assessment of thedecay time and the vibration frequency.

FIG. 26 corresponds to a temporal enlargement of FIG. 25.

FIG. 27 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side two connections of the transmitter (UEB), specifically thethird sub-signal (S2 c) of the second analogue signal (S2) and firstsub-signal (S2 a) of the second analogue signal (S2), areshort-circuited.

Symptoms

The fact that the third sub-signal (S2 c) of the second analogue signal(S2) is short-circuited with the first sub-signal (S2 a) of the secondanalogue signal (S2) means that the ultrasound transducer (TR) is notsufficiently supplied with energy. This error is detectable by anassessment of the decay time and the vibration frequency.

The amplitude at the second sub-signal (S2 b) of the second signal (S2)is also reduced by this short-circuit and may therefore be identified bya fourth comparator (C4) by means of comparison with a fourth reference(Ref4).

A fourth comparator (C4) at the second sub-signal (S2 b) of the secondanalogue signal (S2) (see also FIG. 9) may detect the continuousundershooting of this fourth reference value (Ref4) in the transmissionphase (SP) and/or in the receive phase (EP) by comparison with a fourthreference (Ref4) and may thus conclude that the third sub-signal (S2 c)of the second analogue signal (S2) and the first sub-signal (S2 a) ofthe second analogue signal (S2) might be short-circuited. The setting ofthe corresponding fourth comparison signal (v4) may be identified by the(system) control device (CTR) or the digital input circuit (DSI). Thesethen issue a corresponding error signal or a corresponding errormessage. It should be noted here that the various error cases may bebetter separated by a plurality of different fourth reference values(Ref4) and possibly further forth comparators (C4).

FIG. 28 corresponds to a temporal enlargement of FIG. 27.

FIG. 29 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side two connections of the transmitter (UEB), specifically thethird sub-signal (S2 c) of the second analogue signal (S2) and secondsub-signal (S2 b) of the second analogue signal (S2), areshort-circuited.

Symptoms

The fact that the third sub-signal (S2 c) of the second analogue signal(S2) and the second sub-signal (S2 b) of the second analogue signal (S2)are short-circuited with one another means that the ultrasoundtransducer (TR) is not sufficiently supplied with energy. This error isdetectable by an assessment of the decay time and the vibrationfrequency.

The amplitude at the first sub-signal (S2 a) of the second signal (S2)his likewise reduced by this short-circuit and may therefore beidentified by a sixth comparator (C6) by means of comparison with asixth reference (Ref6).

A sixth comparator (C6) at the first sub-signal (S2 a) of the secondanalogue signal (S2) (see also FIG. 9) may detect the continuousundershooting of this sixth reference value (Ref6) in the transmissionphase (SP) and/or in the receive phase (EP) by comparison with a sixthreference (Ref6) and may thus conclude that the third sub-signal (S2 c)of the second analogue signal (S2) and the second sub-signal (S2 b) ofthe second analogue signal (S2) might be short-circuited. The setting ofthe corresponding sixth comparison signal (v6) may be identified by the(system) control device (CTR) or the digital input circuit (DSI). Thesethen issue a corresponding error signal or a corresponding errormessage. It should be noted here that the various error cases may bebetter separated by a plurality of different sixth reference values(Ref6) and possibly further sixth comparators (C6).

FIG. 30 corresponds to a temporal enlargement of FIG. 29.

FIG. 31 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransducer resistor (R_(TR)) is not connected on the secondary side,that is to say either the first sub-signal (S3 a) of the third analoguesignal (S3) or the second sub-signal (S3 b) of the third analogue signal(S3) is not connected to the transducer resistor (R_(TR)).

The non-connected transducer resistor (R_(TR)) means that the ultrasoundtransducer (TR) may not reduce the vibration energy stored in it withthe start of the decay phase (AP) as quickly as intended. This error istherefore easily detectable by an assessment of the decay time.

FIG. 32 corresponds to a temporal enlargement of FIG. 31.

FIG. 33 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein thetransducer capacitor (C_(TR)) is not connected on the secondary side,that is to say either the first sub-signal (S3 a) of the third analoguesignal (S3) or the second sub-signal (S3 b) of the third analogue signal(S3) is not connected to the transducer capacitor (C_(TR)).

The non-connected transducer capacitor (C_(TR)) results in signalchanges that are only detectable with difficulty. The vibrationfrequency is easily lowered. These changes, however, are only so minimalthat these errors therefore are not reliably detectable by an assessmentof the decay time or the decay frequency.

Detectability, however, may be attained in other ways. To this end, itis necessary to look at FIG. 34 in detail.

FIG. 34 corresponds to a temporal enlargement of FIG. 33. The biggestdifference between the normal case of FIG. 12 and the image in FIG. 34is that the signal at the centre tap of the transmitter (UEB), that isto say the third sub-signal (S2 c) of the second analogue signal (S2),in contrast to the normal case (see FIG. 11), is no longer symmetricalin triangular fashion, and instead has a more sawtooth-shaped profile.For example, a transformation into another signal area is thereforeexpedient for detection of this error. Such a transformation may be, forexample, a Fourier transformation, a discrete Fourier transformation, aLaplace transformation, or a wavelet transformation, etc. For example,it is also conceivable to generate a sawtooth reference signal and atriangular signal of identical frequency by means of a PLL and tomultiply the third sub-signal (S2 c) of the second signal (S2) by thesetwo signals during the transmission phase and then to subject them tolow-pass filtering, that is to say consequently to form a scalar productfrom these two (see also FIGS. 50 to 53). The multiplication by thesawtooth signal should give a result of zero with correct phase positionof the generated sawtooth signal, whereas the multiplication by thetriangular signal should give a value different from zero with correctphase position of the generated sawtooth signal. (Merely for the sake ofcompleteness: a triangular signal is understood to mean a signal with atemporal amplitude profile, wherein this temporal amplitude profile ischaracterised by a direct succession of triangular voltage profiles ofthe signal in question, and wherein these triangles should beapproximately isosceles triangles (see also signal A2 c_b in FIG. 51). Asawtooth signal is understood to mean a signal with a temporal amplitudeprofile, wherein this temporal amplitude profile is characterised by adirect succession of triangular voltage profiles of the signal inquestion, and wherein one limb of such a triangle is significantlysteeper than the other limb (see also signal A2 c_a in FIG. 51). Thissteeper limb is preferably almost vertical with respect to the timeaxis. This calculation may be performed easily in the analogue inputcircuit (AS) as analogue mixer or in the digital input circuit (DSI)).

In this way, a first value for the non-straight signal component in thethird sub-signal (S2 c) of the second signal (S2) and a second value forthe straight signal component in the third sub-signal (S2 c) of thesecond signal (S2) may be determined.

A corresponding comparison apparatus may compare the first value with anassociated reference value for the non-straight signal component and mayprompt the issuing of an error signal if this first value lies above theassociated reference value for the non-straight signal component.

A further corresponding comparison apparatus may compare the secondvalue with an associated reference value for the straight signalcomponent and may prompt the issuing of an error signal if this secondvalue lies below the associated reference value for the straight signalcomponent. This concept is developed in the descriptions of FIGS. 50 to53.

FIG. 35 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side there is no control of the driver for the first sub-signal(S2 a) of the second analogue signal (S2) in the driver stage (DR).

This error may occur for example when the driver transistor for thefirst sub-signal (S2 a) of the second signal (S2) in the driver unit(DR) is not functioning. This transistor is then unable to pull thefirst sub-signal (S2 a) of the second analogue signal (S2) to ground.

One possibility for ascertaining this error is to check this “pulling toground” of the relevant transistor a few ps after this transistor hasbeen switched on, with the aid of the sixth comparator (C6). To thisend, the sixth comparator (C6) (see FIG. 9) compares the voltage levelat the first sub-signal (S2 a) of the second signal (S2) with a sixthreference value (Ref6). If this is not undershot at this moment in timeshortly after the switching on of the transistor, there is thus an errorpresent.

Another possibility lies again in the analysis of the straight andnon-straight signal component, as presented in the description of FIG.34, however now it is the first sub-signal (S2 a) of the second analoguesignal (S2) that is analysed.

A further possibility lies in the fact that, on account of the symmetryof the apparatus, the signal profile of the first sub-signal (S2 a) ofthe second signal (S2) and the signal profile of the second sub-signal(S2 b) of the second signal (S2) must be the same as one another apartfrom a phase shift of 180° (a transmitter (UEB) according to FIG. 7 ispresupposed). It is therefore conceivable, in one or more periods, todetect one or more values of the signal profile of the first sub-signal(S2 a) of the second signal (S2) at certain moments in time and todetect, phase-shifted by 180° thereto at the corresponding moments intime, one or more values of the signal profile of the second sub-signal(S2 b) of the second signal (S2) at certain moments in time and to thencalculate and sum the differences of the corresponding pairs formed ineach case of a value of the signal profile of the first sub-signal (S2a) of the second signal (S2) and a value of the signal profile of thesecond sub-signal (S2 b) of the second signal (S2) at the correspondingmoments in time. If the difference or the value of the differenceovershoots a predetermined value, the symmetry of the apparatus is thusdisrupted, and an error signal may be triggered. This calculation ispreferably performed in the digital input circuit (DSI) or in thecontrol device (CTR). Such an apparatus is then suitable for detectingthe symmetry of two sub-signals (S2 a, S2 b) of the second analoguesignal (S2). This concept will be explained in greater detail inconjunction with FIG. 49.

FIG. 36 corresponds to a temporal enlargement of FIG. 35.

FIG. 37 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side the driver for the first sub-signal (S2 a) of the secondanalogue signal (S2) is short-circuited to ground in the driver stage(DR).

Symptoms

The driver short-circuited to ground on the primary side for the firstsub-signal (S2 a) of the second analogue signal (S2) in the driver stage(DR) means that the ultrasound transducer (TR) is not sufficientlysupplied with energy. This error is detectable by an assessment of thedecay time and the vibration frequency.

FIG. 38 corresponds to a temporal enlargement of FIG. 37.

FIG. 39 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side there is no control of the driver for the second sub-signal(S2 b) of the second analogue signal (S2) in the driver stage (DR).

This error may occur for example if the driver transistor for the secondsub-signal (S2 b) of the second signal (S2) in the driver unit (DR) isnot functioning. This transistor is then unable to Paul the secondsub-signal (S2 b) of the second analogue signal (S2) to ground.

One possibility for ascertaining this error is to check this “pulling toground” of the relevant transistor a few ps after this transistor hasbeen switched on, with the aid of the fourth comparator (C4). To thisend, the fourth comparator (C4) (see FIG. 9) compares the voltage levelat the second sub-signal (S2 b) of the second signal (S2) with a fourthreference value (Ref4). If this is not undershot at this moment in timeshortly after the switching on of the transistor, there is thus an errorpresent.

Another possibility lies again in the analysis of the straight andnon-straight signal component, as presented in the description of FIG.34, however now it is the second sub-signal (S2 b) of the secondanalogue signal (S2) that is analysed.

A further possibility lies in the fact that, on account of the symmetryof the apparatus, the signal profile of the first sub-signal (S2 a) ofthe second signal (S2) and the signal profile of the second sub-signal(S2 b) of the second signal (S2) must be the same as one another apartfrom a phase shift of 180° (a transmitter (UEB) according to FIG. 7 ispresupposed). It is therefore conceivable, in one or more periods, todetect one or more values of the signal profile of the first sub-signal(S2 a) of the second signal (S2) at certain moments in time and todetect, phase-shifted by 180° thereto at the corresponding moments intime, one or more values of the signal profile of the second sub-signal(S2 b) of the second signal (S2) at certain moments in time and to thencalculate and sum the differences of the corresponding pairs formed ineach case of a value of the signal profile of the first sub-signal (S2a) of the second signal (S2) and a value of the signal profile of thesecond sub-signal (S2 b) of the second signal (S2) at the correspondingmoments in time. If the difference or the value of the differenceovershoots a predetermined value, the symmetry of the apparatus is thusdisrupted, and an error signal may be triggered. This calculation ispreferably performed in the digital input circuit (DSI) or in thecontrol device (CTR). Such an apparatus is then suitable for detectingthe symmetry of two sub-signals (S2 a, S2 b) of the second analoguesignal (S2). This concept will be explained in greater detail inconjunction with FIG. 49.

FIG. 40 corresponds to a temporal enlargement of FIG. 39.

FIG. 41 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side the driver for the second sub-signal (S2 b) of the secondanalogue signal (S2) is short-circuited to ground in the driver stage(DR).

Symptoms

The driver short-circuited to ground on the primary side for the secondsub-signal (S2 b) of the second analogue signal (S2) in the driver stage(DR) means that the ultrasound transducer (TR) is not sufficientlysupplied with energy. This error is detectable by an assessment of thedecay time and the vibration frequency.

FIG. 42 corresponds to a temporal enlargement of FIG. 41.

FIG. 43 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side there is no control of the driver for the third sub-signal(S2 c) of the second analogue signal (S2) in the driver stage (DR).

The resultant error image may be detected both by an assessment of thedecay time and by a measurement with the aid of a sixth comparator (C6)at the first sub-signal (S2 a) of the second analogue signal (S2).

FIG. 44 corresponds to a temporal enlargement of FIG. 43.

FIG. 45 shows important signals (d1, S2 c, S2 a, S2 b, S5) whentransmitting an ultrasound burst in the operating mode, wherein on theprimary side the driver for the third sub-signal (S2 c) of the secondanalogue signal (S2) is short-circuited to ground in the driver stage(DR).

In the event of a low-resistance short circuit of the driver transistor,the transmission current is significantly increased. This may bedetected on the basis of the decay time.

Detection by a sixth comparator (C6), however, by comparison of thefirst sub-signal (S2 a) of the second signal (S2) with a sixth referencevalue (Ref6) in the receive phase (EP) is particularly advantageous. Inthe normal case the level there is zero. In this error case the levelthere is increased. This may be detected by assessing the sixthcomparison signal (v6) generated during the comparison and may be usedas a triggering event for generating an error signal by the digitalinput circuit (DSI) or the (system) control device (CTR).

Detection by a fourth comparator (C4), however, by comparison of thesecond sub-signal (S2 b) of the second signal (S2) with a fourthreference value (Ref4) in the receive phase (EP) is also advantageous.In the normal case the level there is zero. In this error case the levelthere is increased. This may be detected by assessing the fourthcomparison signal (v4) generated during the comparison and may be usedas a triggering event for generating an error signal by the digitalinput circuit (DSI) or the (system) control device (CTR).

FIG. 46 corresponds to a temporal enlargement of FIG. 45.

FIG. 47 shows the preferred test procedure of a self-test of theproposed measuring system (SS). Once the proposed measuring system (SS)has been switched on or reset, the proposed measuring system (SS) is ina switched-on mode (EZ). In this switched-on mode (EZ), the proposedmeasuring system (SS) preferably does not output any measured values,but only status messages regarding the progress of the switch-onprocedure via the data interface (IO).

The proposed measuring system (SS) then changes into the third test mode(3.TZ). In this mode, the proposed measuring system (SS) tests thecorrect functioning of the digital signal generating unit (DSO) and ofthe digital input circuit (DSI). The signal profile corresponds here toFIG. 5. The digital signal generating unit (DSO) generates predeterminedtest patterns and test sequences. In particular, criticalsafety-relevant error cases may be simulated. In this regard, it maythen be checked whether the digital input circuit (DSI) respondscorrectly in safety-relevant fashion and correctly detects the simulatedsafety-relevant errors. Conversely, the signal generation by the digitalsignal generating unit (DSO) may be checked. In this way, the digitalsignal generating unit (DSO) and digital input circuit (DSI) check,preferably in accordance with requirements of the control device (CTR),all test cases for the digital signal path. If an error occurs, theproposed measuring system (SS) thus preferably changes into an errormode (FZ), which may not be left easily and in which there are typicallyno measured values or measurement results forwarded to superordinateunits without special marking.

In this regard, the switched-on mode (EZ) is incidentally a specificerror mode (FZ). A plurality of error modes may thus also be provided,which are assumed depending on the determined error. The purely digitaltest has the advantage that here the gates may be precisely checked, andtherefore the failure of individual gates is identifiable. The testcoverage of the self-test of these circuit parts is increased.

If, however, all checks in the third test mode (3.TZ) are performedsuccessfully, the proposed measuring system thus switches into thesecond test mode (2.TZ). The internal signal path of the proposedmeasuring system (SS) is hereby now modified such that it corresponds toFIG. 4. The internal signal path of the proposed measuring system (SS)here by now also comprises the analogue circuit parts. If an error nowoccurs, this may thus be attributed to the analogue circuit parts, sincethe digital circuit parts have already been deemed to be “error-free”.As before, the digital signal generating unit (DSO) and the digitalinput circuit (DSI) in this way again check, preferably in accordancewith specifications by the control device (CTR), all test cases for theanalogue and digital signal path, which are now combined. If an erroroccurs, the proposed measuring system (SS) thus preferably changes backinto an error mode (FZ) which may not be easily left and in which thereare typically no measured values or measurement results forwarded tosuperordinate units without special marking. The digital signalgenerating unit (DSO) again generates predetermined test patterns andtest sequences which are tailored to this combined analogue/digitalsignal path in the second test mode. In particular, criticalsafety-relevant error cases may again be simulated. In this regard, itmay then be checked whether the digital input circuit (DSI) incombination with the analogue input circuit (AS) responds correctly insafety-relevant fashion and correctly detects the simulatedsafety-relevant errors. Conversely, the signal generation may checkwhether the digital signal generating unit (DSO) and the driver stage(DR) function correctly. Furthermore, various safety-relevantconfigurations of a possible subsequent transmission channel may besimulated, and the simulation results may be assessed.

If, however, all checks in the second test mode (2.TZ) are performedsuccessfully, the proposed measuring system (SS) thus changes into thefirst test mode (1.TZ). The internal signal path of the proposedmeasuring system (SS) is now hereby modified such that it corresponds toFIG. 3. The signal path thus now comprises also the measuring unit (TR),that is to say typically the ultrasound transducer (TR), and themeasuring channel (CN).

The digital signal generating unit (DSO) now generates test signals andtest patterns, which, once they have passed through the signal path andreach the measuring unit (TR), that is to say the ultrasound transducer(TR), interact therewith. The response signal of the measuring unit(TR), that is to say the ultrasound transducer (TR), is fed into thereturning signal path and, once it has passed through this signal path,is assessed by the digital input circuit (DSI).

In addition, it is expedient, especially in this first test mode (1.TZ),to monitor the signals of the measuring unit (TR), that is to say theultrasound transducer (TR), for example by comparators or otherapparatuses. Here as well, the digital signal generating unit (DSO) maygenerate particularly critical test signals and test patterns forparticularly safety-relevant cases. If an error occurs, the proposedmeasuring system thus changes back into an error mode (FZ). The checksmay include, for example, amplitudes, amplitude differences (with andwithout phase shift) and signal components such as harmonic components.

FIG. 48 corresponds to the greatest possible extent to FIG. 8, with thedifference that FIG. 48 does not comprise the comparators (C1, C2, C3)or the difference amplifier (D1). These, however, may be combined withFIG. 48. FIG. 48 makes use of the fact that the measuring unit (TR),that is to say the ultrasound transducer (TR), and the transmitter (UEB)are generally embodied symmetrically. This symmetry, in reality, is notperfect, and therefore the symmetry comparison must be provided with athreshold value.

In FIG. 48 a first symmetry checking apparatus (SBA) is thereforeprovided, which checks the symmetry of two or more sub-signals (S2 a, S2b, S2 c) of the second analogue signal (S2) and generates acorresponding thirteenth comparison result signal (v13) depending on theresult of this comparison. The first symmetry checking apparatus (SBA)preferably implements internal phase shifts in such a way that theresultant shifted sub-signals should match.

Furthermore, a second symmetry checking apparatus (FPB) is provided inFIG. 48 and checks the symmetry of two (or possibly more—not discussedhere) sub-signals (S3 a, S3 b) of the third analogue signal (S3) andgenerates a corresponding fourteenth comparison result signal (v14)depending on the result of this comparison. The second symmetry checkingapparatus (FPB) preferably likewise implements internal phase shifts asappropriate, in such a way that the resultant shifted sub-signals shouldmatch. This check preferably takes place only in the transmission phase(SP). A phase shift of 180° corresponds here to an inversion, forexample by an inverting amplifier with amplification −1. In this regard,such an inverting amplifier is also a phase shifter in the sense of thisdisclosure when a phase shift of 180° is required.

FIG. 49 shows the apparatus corresponding to FIG. 48 with specificexemplary embodiment of a symmetry check for the secondary side of thetransmitter (UEB). The second symmetry checking apparatus (SPB) isconnected to the first sub-signal (S3 a) of the third analogue signal(S3) and the second sub-signal (S3 b) of the third analogue signal (S3).A precondition for the use of this second symmetry checking apparatus(SPB) is that, firstly, the signal path part formed of transmitter(UEB), ultrasound transducer (TR) and ultrasound channel (CN) isconstructed absolutely symmetrically and, secondly, is loadedsymmetrically by the analogue multiplexer (AMX) and the analogue inputcircuit (AS), and, thirdly, is controlled symmetrically by the driverstage (DR) and the first sub-signal (S2 a) of the second analogue signal(S2), the second sub-signal (S2 b) of the second analogue signal (S2)and the third sub-signal (S2 c) of the second analogue signal (S2). Apreferred exemplary symmetrical control by these sub-signals of thesecond analogue signal (S2) may be inferred from FIG. 12. The secondsymmetry checking apparatus (SPB) is marked in FIG. 49 by a dashed box.It comprises a first phase shifter (S&H_Ba), which is preferablyembodied as a holding circuit, and at a first moment in time (Z1)buffers the momentary value of the first sub-signal (S3 a) Of the thirdanalogue signal (S3) and outputs it as first sub-signal (S3 am) of thethird buffered signal (S3 m). It comprises a second phase shifter(S&H_Bb), which is likewise preferably embodied as a holding circuit,and at a second moment in time (Z2) buffers the momentary value of thesecond sub-signal (S3 b) of the third analogue signal (S3) and outputsit as second sub-signal (S3 bm) of the third buffered signal (S3 m). Itis now presupposed that the first sub-signal (S3 a) of the thirdanalogue signal (S3) and the second sub-signal (S3 b) of the thirdanalogue signal (S3) are periodic and have a vibration period (T),wherein the first sub-signal (S3 a) of the third analogue signal (S3) isphase-shifted in relation to the second sub-signal (S3 b) of the thirdanalogue signal (S3) by 180° (=n), that is to say is the inversionthereof. The temporal distance between the first moment in time (Z1) andthe second moment in time (Z2) is selected such that it corresponds tothe value (n+0.5)*T, wherein n is a positive integer or zero. A fifthdifference amplifier (D5) forms the fifth difference signal (d5) fromthe first sub-signal (S3 am) of the third buffered signal (S3 m) and thesecond sub-signal (S3 bm) of the third buffered signal (S3 m). A secondintegrator (INT2), which may also be a low-pass filter, integrates thefifth difference signal (d5) to form an integrated fifth differencesignal (d5 i). The second integrator (INT2) is preferably deleted againafter m clock periods (T), wherein m is a positive integer. The fifthdifference signal (d5) is preferably rectified, such that only theamplitude of the fifth difference signal (d5) is integrated. Theintegrated fifth difference signal (d5 i) is then a measure for theasymmetry within the m clock periods (T). A fourteenth comparator (C-14)compares the integrated fifth difference signal (d5 i) with a 14reference value (Ref14) and generates the fourteenth comparison resultsignal (v14). This is assessed typically by the digital input circuit(DSI) and/or the control device (CTR), which generate an error messageas appropriate. This check is preferably performed only in thetransmission phase (SP).

If the integrated fifth difference signal (d5 i) is intended torepresent a minimum measure for the symmetry, the fifth differencesignal (d5 i), multiplied by −1, must be output by the fifth differenceamplifier (D5) and the second integrator (INT2) not deleted again afterm clock periods (T), but instead preloaded to a positive preload value.If the integrated fifth difference signal (d5 i) undershoots thefourteenth reference value (Ref14), the fourteenth comparator (C14) thusgenerates the fourteenth comparison result signal (v14), so as to signalan inadequate symmetry.

FIG. 50 shows the apparatus corresponding to FIG. 48 with specificembodiment of a symmetry check for the primary side of the transmitter(UEB). The first symmetry checking apparatus (SPA) is connected to thefirst sub-signal (S2 a) of the second analogue signal (S2) and thesecond sub-signal (S2 b) of the second analogue signal (S2). Aprecondition for the use of this first symmetry checking apparatus (SPA)is that, firstly, the signal path part formed of transmitter (UEB),ultrasound transducer (TR) and ultrasound channel (CN) is constructedabsolutely symmetrically and, secondly, is loaded symmetrically by theanalogue multiplexer (AMX) and the analogue input circuit (AS), and,thirdly, is controlled symmetrically by the driver stage (DR) and thefirst sub-signal (S2 a) of the second analogue signal (S2), the secondsub-signal (S2 b) of the second analogue signal (S2) and the thirdsub-signal (S2 c) of the second analogue signal (S2) in the normal case.A preferred exemplary symmetrical control by these sub-signals of thesecond analogue signal (S2) may be inferred from FIG. 12. The firstsymmetry checking apparatus (SPA) is marked in FIG. 50 by a dashed box.It comprises a first phase shifter (S&H_Aa), which is preferablyembodied as a holding circuit, and at a first moment in time (Z1)buffers the momentary value of the first sub-signal (S2 a) Of the secondanalogue signal (S2) and outputs it as first sub-signal (S2 am) of thesecond buffered signal (S2 m). It comprises a second phase shifter(S&H_Ab), which is likewise preferably embodied as a holding circuit,and at a second moment in time (Z2) buffers the momentary value of thesecond sub-signal (S2 b) of the second analogue signal (S2) and outputsit as second sub-signal (S2 bm) of the second buffered signal (S2 m). Itis now presupposed that the first sub-signal (S2 a) of the secondanalogue signal (S2) and the second sub-signal (S2 b) of the secondanalogue signal (S2) are periodic and have a vibration period (T),wherein the first sub-signal (S2 a) of the second analogue signal (S2)is phase-shifted in relation to the second sub-signal (S2 b) of thesecond analogue signal (S2) by 180° (=n), that is to say is theinversion thereof. The temporal distance between the first moment intime (Z1) and the second moment in time (Z2) is selected such that itcorresponds to the value (n+0.5)*T, wherein n is a positive integer orzero. A sixth difference amplifier (D6) forms the sixth differencesignal (d6) from the first sub-signal (S2 am) of the second bufferedsignal (S2 m) and the second sub-signal (S2 bm) of the second bufferedsignal (S2 m). A second integrator (INT1), which may also be a low-passfilter, integrates the sixth difference signal (d6) to form anintegrated sixth difference signal (d6 i). The first integrator (INT1)is preferably deleted again after m clock periods (T), wherein m is apositive integer. The sixth difference signal (d6) is preferablyrectified, such that only the amplitude of the sixth difference signal(d6) is integrated. The integrated sixth difference signal (d6 i) isthen a measure for the asymmetry within the m clock periods (T). Athirteenth comparator (C13) compares the integrated sixth differencesignal (d6 i) with a thirteenth reference value (Ref13) and generatesthe thirteenth comparison result signal (v13). This is assessedtypically by the digital input circuit (DSI) and/or the control device(CTR), which generate an error message as appropriate. This check ispreferably performed only in the transmission phase (SP).

If the integrated sixth difference signal (d6 i) is intended torepresent a minimum measure for the symmetry, the sixth differencesignal (d6 i), multiplied by −1, must be output by the sixth differenceamplifier (D6) and the first integrator (INT1) not deleted again after mclock periods (T), but instead preloaded to a positive preload value. Ifthe integrated sixth difference signal (d6 i) undershoots the thirteenthreference value (Ref13), the thirteenth comparator (C13) thus generatesthe thirteenth comparison result signal (v13), so as to signal aninadequate symmetry.

FIG. 51 compares, by way of example, the undisturbed third sub-signal(S2 c) of the second analogue signal (S2) (see also FIG. 11) with thedisturbed third sub-signal (S2 c) of the second analogue signal (S2)with a capacitor disconnection of the transducer capacitor (C_(TR)) (seeFIG. 34) and shows exemplary analysis signals.

It can be seen that the symmetrical form of the undisturbed thirdsub-signal (S2 c) of the second analogue signal (S2) converts into amore sawtooth-shaped form in the form of the disturbed third sub-signal(S2 cLC(of the second analogue signal (S2) by the disconnection of thetransducer capacitor (C_(TR)). The disturbed third sub-signal (S2 cLC)of the second analogue signal (S2) clearly has a harmonic. The basicconcept for detecting this error is therefore to generate twocoefficients by forming, periodically, a first scalar product between asuitable first internal analysis signal (A_a) and the signal (ZA) to beanalysed on the one hand and by forming, periodically, a second scalarproduct between a suitable second internal analysis signal (A_a) and thesignal (ZA) to be analysed on the other hand, that is to say a firstinternal coefficient signal (s3 a) and a second internal coefficientsignal (s3 b), and by comparing these with one another and, in the eventof deviations from the expected value, generating an internal comparisonsignal (v_X), which may then be assessed by the control device (CTR)and/or the digital input circuit (DSI) in order to generate an errormessage. In the specific case of FIG. 51, two possible analysis signalsfor analysis of the second sub-signal (S2 c) of the second analoguesignal (S2) are proposed by way of example. The first analysis signalpair consists of two digital signals, which may be generated preferablyand particularly easily in the digital signal generating unit (DSO).These are a first exemplary analysis signal (A2 c_a) for the coefficientmonitoring in the coefficient monitoring sub-apparatus (KUE2 c) for thethird sub-signal (S2 c) of the second analogue signal (S2) and a secondexemplary analysis signal (A2 c_b) for the coefficient monitoring in thecoefficient monitoring sub-apparatus (KUE2 c) for the third sub-signal(S2 c) of the second analogue signal (S2). The first exemplary analysissignal (A2 c_a) in this example is more similar to the disturbed thirdsignal (S2 cLC) of the second analogue signal (S2). The second exemplaryanalysis signal (A2 c_b) in this example is more similar to theundisturbed third sub-signal (S2 c) of the second analogue signal (S2).In this example the first exemplary analysis signal (A2 c_a) isphase-shifted by −90° in relation to the second exemplary analysissignal (A2 c_b). In this example, these are glass sinusoidal-like andcosinusoidal-like signals. When developing the proposal it wasidentified that a disconnection of the transducer capacitor (C_(TR))changes the configuration of the inherent vibration frequencies of thesystem, which is still symmetrical per se, formed of the transmitter(UEB), transducer resistor (R_(TR)), “transducer capacitor (C_(TR))” andin a transducer (TRi), such that no longer is only the fundamentalvibration present, but other vibration modes are then also excited. Ifsinusoidal-shaped and cosinusoidal-shaped signals were used, the firstinternal coefficient signal (s3 a) and the second internal coefficientsignal (s1 b) would correspond the Fourier coefficients.

Furthermore, FIG. 52 shows an alternative pair of possible analysissignals. What are shown are an alternative first exemplary analysissignal (A2 c_a′) for the coefficient monitoring in the coefficientmonitoring sub-apparatus (KUE2 c) for the third sub-signal (S2 c) of thesecond analogue signal (S2) and an alternative second exemplary analysissignal (A2 c_b′) for the coefficient monitoring in the coefficientmonitoring sub-apparatus (KUE2 c) for the third sub-signal (S2 c) of thesecond analogue signal (S2). The alternative first exemplary analysissignal (A2 c_a′) in this example is a sawtooth signal and is thus moresimilar to the disturbed third sub-signal (S2 cLC) of the secondanalogue signal (S2). The alternative second exemplary analysis signal(A2 c_b′) in this example is a triangular signal and is thus moresimilar to the undisturbed third sub-signal (S2 c) of the secondanalogue signal (S2). In contrast to the previous example, however, inrelation to the implementation of the scalar products proposed in FIG.52, the alternative first exemplary analysis signal (A2 c_a′) for thecoefficient monitoring in the coefficient monitoring sub-apparatus (KUE2c) for the third sub-signal (S2 c) of the second analogue signal (S2)and the alternative second exemplary analysis signal (A2 c_b′) for thecoefficient monitoring in the coefficient monitoring sub-apparatus (KUE2c) for the third sub-signal (S2 c) of the second analogue signal (S2)are no longer orthogonal to one another. Rather, they contain componentsof one another in respect of this scalar product. The analysis signalsmay also be understood as a stringing together ofanalysis-signal-specific wavelets.

The alternative first exemplary analysis signal (A2 c_a′) for thecoefficient monitoring in the coefficient monitoring sub-apparatus (KUE2c) for the third sub-signal (S2 c) of the second analogue signal (S2)then consists of a temporal stringing together of individualsawtooth-shaped wavelets, wherein one wavelet would comprise one tooth.

The alternative second exemplary analysis signal (A2 c_b′) thecoefficient monitoring in the coefficient monitoring sub-apparatus (KUE2c) for the third sub-signal (S2 c) of the second analogue signal (S2)then consists of a temporal stringing together of individual triangularwavelets, wherein one wavelet would comprise an isosceles triangle.

Depending on the purpose of the analysis, other wavelets may also beselected. Since errors at the transmitter (UEB), the transducer resistor(R_(TR)), the transducer capacitor (C_(TR)) and the inner transducer(TRi) do not always destroy the symmetry, the change to the spectralproperties of the combination of these components may be monitored inthis way.

It is thus possible, inter alia, to reliably detect largely symmetricaltransmitter short circuits of the transmitter (UEB), deviations of theeffective resistance of the transducer resistor (R_(TR)), changes to theeffective capacitance of the transducer capacitor (C_(TR)) and changesto the impedance of the inner ultrasound transducer (TRi) if these haveeffects on relevant spectral properties of the combination of thesecomponents.

FIG. 52 shows, by way of example, a possible inner structure of ananalogue coefficient-monitoring sub-apparatus (KUE). Otherimplementations are possible. The signal to be analysed (ZA) ismultiplied in this example by the first multiplier (M1) by the firstinternal analysis signal (A_a) to give the first filter input signal (s1a) and in the second multiplier (M2) to give the second filter inputsignal (s1 b). The first analysis signal (A_a) for example mayassimilate the normal operating case, whereas the second analysis signal(A_b) for example may assimilate a defective operating case. The firstfilter input signal (s1 a) is filtered by the first filter (F1) to givethe first filter output signal (s2 a). The first filter (F1) ispreferably an integrator or low-pass filter. The second filter inputsignal (s1 b) is filtered by the second filter (F2) to give the secondfilter output signal (s2 b). The first filter (F1) is preferably anintegrator or low-pass filter. The first internal sample-and-hold unit(S&H_Ca) samples the first internal filter output signal (S2 a) at thetemporal end (FIG. 51: for example moments in time z1, z2, z3, z4) ofone or more complete periods T of the signal to be analysed (ZA) (seeFIG. 1) and thus forms the first internal coefficient signal (S3 a). Thesecond internal sample-and-hold unit (S&H_Cb) samples the secondinternal filter output signal (S2 b) at the temporal end (FIG. 51: forexample moments in time z1, z2, z3, z4) of one or more complete periodsT of the signal to be analysed (ZA) (see FIG. 51), and thus forms thesecond internal coefficient signal (S3 b).

These samples are preferably taken only in the transmission phase (SP)or at selected time periods within the transmission phase (SP). Thefirst internal sample-and-hold unit (S&H_Ca) and of the second internalsample-and-hold unit (S&H_Cb) are controlled preferably by the digitalsignal generating unit (DSO).

The angle calculation unit (arctan) generates the angle signal (sα) fromthe first internal coefficient signal (S3 a) and the second internalcoefficient signal (S3 b). The angle signal (sα) preferably representsthe arctan or the acrccot of the ratio of the level of the firstinternal coefficient signal (S3 a) and of the second internalcoefficient signal (S3 b). Approximations and other assessments (forexample simple division, etc.) are conceivable.

The internal comparator (C_X) compares the level of the angle signal(sα) with the internal reference value (Ref_X). Depending on the resultof this comparison, the internal comparator (C_X) generates an internalcomparison result signal (V_X).

FIG. 52 shows an exemplary structure for the realisation of thecorresponding coefficient monitoring sub-apparatuses with the referencesigns KUE2 a, KUE2 b, KUE2 c, KUE3 a and KUE3 b in FIG. 53. Otherrealisations, in particular partially and wholly digital realisations,for example as a program in signal processors, are conceivable.

It is, of course, conceivable to use more than two analysis signals(A_a, A_b) and to generate more than two coefficient signals via morethan two parallel signal paths accordingly and to perform morecomparisons accordingly, which leads to many more comparison resultsignals, which, again, may be assessed by the control device (CTR)and/or the digital receive circuit (DSI) and may be used for thegeneration of error messages.

FIG. 53 corresponds to FIG. 8, wherein the level monitorings are notshown. Instead, possible coefficient-monitoring sub-apparatuses areshown, with the reference signs KUE2 a, KUE2 b, KUE2 c, KUE3 a and KUE3b in FIG. 53. Different comparison result signals are generated (v15,v16, v17, v18, v19) depending on the monitored signal and are preferablyassessed by the digital input circuit (DSI) and/or the (system) controldevice, which trigger an error message as appropriate.

FIG. 54 corresponds to FIG. 52, wherein two comparators for additionalmonitoring of the two internal coefficient signals, i.e. for the firstinternal coefficient signal (s3 a) and the second internal coefficientsignal (s3 b), are now provided. Three comparison result signals (V_X,V_Y, V_Z) are now generated instead of just one comparison result signal(V_X). FIG. 54 thus shows, by way of example, a further possible innerstructure of an analogue coefficient monitoring sub-apparatus (KUE).

A second internal comparator (C_Y) compares the first internalcoefficient signal (s3 a) with a second internal reference value (R_Y).Depending on the comparison result, the second internal comparator (C_Y)generates a second internal comparison result signal (V_Y), which, asbefore, is assessed typically by the control device (CTR) and/or thedigital input circuit (DSI), so as to generate an error message asappropriate.

A third internal comparator (C_Z) compares the second internalcoefficient signal (s1 b) with a third internal reference value (R_Z).Depending on the comparison result, the third internal comparator (C_Z)generates a third internal comparison result signal (V_Z), which, asbefore, is assessed typically by the control device (CTR) and/or thedigital input circuit (DSI), so as to generate an error message asappropriate.

FIG. 55 corresponds to FIG. 54, wherein the ratio of the two internalcoefficient signals is now not monitored. Only two comparison resultssignals (V_Y, V_Z) are now generated. FIG. 55 thus shows, by way ofexample, a further possible inner structure of an analogue coefficientmonitoring sub-apparatus (KUE). The function of the remaining circuitparts has already been described in the descriptions of FIGS. 52 and 54.

FIG. 56 corresponds to FIG. 55, wherein only one internal coefficientsignal (here s3 a) is now monitored. Only one comparison result signal(V_Y) is now generated. This second comparison result signal (V_Y),however, monitors only the absolute level of the first internalcoefficient signal (s3 a), which corresponds to a monitoring of thefundamental waves or harmonic amplitude. In FIG. 52 the ratio of twocoefficient signals was monitored. FIG. 56 thus shows, by way ofexample, a further possible inner structure of an analogue coefficientmonitoring sub-apparatus (KUE). The function of the remaining circuitparts has already been described in the descriptions of FIGS. 52 and 54.

FIG. 57 corresponds to FIG. 2, with the difference that the thirdanalogue signal (S3) is split before the analogue multiplexer (AMX) byan analogue filter or an analogue amplifier (AV) into the third analoguesignal (S3) and the amplified third analogue signal (S3′). This has theadvantage that an over modulation is avoided. The disadvantage is thatin the second test mode the third analogue test signal (S3 t) is fedback into the signal path via the analogue multiplexer (AMX) only afterthe analogue filter or analogue amplifier (AV). This has the result thatthe analogue filter or the analogue amplifier (AV) is not also tested.Of course, the totality of analogue input circuit (AS), analoguemultiplexer (AMX) and analogue filter or analogue amplifier (AV) couldalso be considered to be a common analogue input circuit having twoinputs, as has already been mentioned above. Should the amplitude of thesecond analogue signal (S2) the small enough for the input of theanalogue multiplexer (AMX) and the input of the analogue input circuit(AS) to not be over modulated by direct application of the secondanalogue signal (S2), the analogue channel simulation unit (ACS) mayoptionally be spared in this configuration. There are thus, in total, atleast three possibilities for preventing an over modulation of theanalogue signal path in the second test mode:

Reconfiguration of the driver stage (DR) in the second test modepreferably by the control device (CTR) in such a way that the outputamplitude of the driver stage (DR) is matched to the maximum inputamplitude of the analogue multiplexer (AMX) and the maximum inputamplitude of the analogue input circuit (AS). In this case, the analoguechannel simulation units may be replaced in some circumstances by wirebridges.

Damping of the second analogue signal (S2) to give the third analoguetest signal (S3 t) in the analogue channel simulation unit in such a waythat the output amplitude of the driver stage (DR) is matched to themaximum input amplitude of the analogue multiplexer (AMX) and themaximum input amplitude of the analogue input circuit (AS).

Omission of a preliminary stage of the analogue input circuit (AS)—inthe example of FIG. 57 of an analogue filter or analogue amplifier (AB)and feeding of the third analogue test signal (S3 t) or even directfeeding of the second analogue signal (S2) via the analogue multiplexer(AMX) into the analogue input circuit (AS). Here, it should again beensured that the output amplitude of the driver stage (DR) is matched tothe maximum input amplitude of the analogue multiplexer (AMX) and themaximum input amplitude of the analogue input circuit (AS). In thiscase, the analogue channel simulation unit may be replaced in somecircumstances by wire bridges.

The corresponding configuration of the measuring system (SS) ispreferably implemented again by the control device (CTR).

To conclude the description of the figures, it should again be mentionedthat in particular the measures of FIGS. 6, 8, 9, 10, 48, 49, 50 and 53may be combined with one another. A person skilled in the art will alsochoose, from these measures, those that come closest to the intendedpurpose so as not to have to carry out all measures for error detection.

Glossary

Frequency Sweep

-   -   A frequency sweep, in the sense of this disclosure, is        understood to mean a process in which the frequency of a first        digital signal (S1) or the frequency of a second analogue signal        (S2) the frequency of an output signal (MS) at a first moment in        time has a starting frequency and at a second moment in time has        an end frequency. The frequency, between the first and the        second moments in time, preferably passes through all        frequencies lying between the starting frequency and the end        frequency, preferably strictly monotonically, but at least        monotonically.

Ultrasound Transducer

-   -   An ultrasound transducer, in the sense of this disclosure, is        composed of the optional (but preferably provided) transducer        resistor (R_(TR)), the optional (but preferably provided)        transducer capacitor (C_(TR)), and the inner ultrasound        transducer (TRi), which comprises the actual vibration element,        housing thereof, and the contacts. An ultrasound transducer is        able to transmit and receive ultrasound signals, preferably in a        time division multiplex.

Test Case/Check Case

-   -   A test case or check case, in the sense of this disclosure, is        understood to mean a predetermined configuration of the signal        path and all of its components. The configuration is implemented        preferably by the control device (CTR). The stimulation of this        predetermined signal path is performed substantially by        predetermined signals of the digital signal generating unit        (DSO). These predetermined signals are monitored within the        signal path by predetermined monitoring apparatuses (for example        difference amplifiers and/or comparators), and the response of        the signal path to such a stimulus is assessed        test-case-specifically, preferably by the digital input circuit        (DSI) or the (system) control device (CTR).

Test Mode

-   -   A test mode is understood to mean a mode of the measuring system        (SS) which is used to check the measuring system (SS) and which        is not the operating mode.

Signal String

-   -   A signal string is understood to mean the forwarding of a signal        within a string of apparatus parts of the measuring system (SS)        along the signal path (see also FIGS. 3, 4 and 5).

Digital Part of the Signal String

-   -   The digital part of the signal string is understood to mean the        circuit parts which are embodied predominantly on the basis of        digital circuit technology. In the present example, these are        the digital signal generating unit (DSO), the digital        multiplexer (DMX) and the digital input circuit (DSI). The        digital channel simulation unit (DCS) may be considered to be        part of the digital signal string in the third test mode.

Analogue Part of the Signal String

-   -   The analogue part of the signal string will be understood to        mean the circuit parts which are embodied predominantly on the        basis of analogue circuit technology. In the present example        these are the driver stage (DR), the analogue multiplexer (AMX),        and the analogue input circuit (AS). The analogue channel        simulation unit (ACS) may be considered to be part of the        analogue signal string in the second test mode.

Error Messages

-   -   In the sense of this disclosure, error messages are formed of        information regarding detected errors that is transmitted via        corresponding apparatus parts, for example cables, or is        provided to predetermined or determinable points in apparatus        parts. The provision of such information is a generation in the        sense of this disclosure.

Triangular Signal

-   -   A triangular signal is understood to mean a signal having a        temporal amplitude profile, wherein this temporal amplitude        profile is characterised by a direct succession of triangular        voltage profiles of the signal in question, and wherein these        triangles should be approximately isosceles triangles (see also        signal A2 c_b in FIG. 51).

Sawtooth Signal

-   -   A sawtooth signal is understood to mean a signal having a        temporal amplitude profile, wherein this temporal amplitude        profile is characterised by a direct succession of triangular        voltage profiles of the signal in question, and wherein one limb        of such a triangle is much steeper than the other limb (see also        signal A2 c_a in FIG. 51).

LIST OF REFERENCE SIGNS

-   1.TZ first test mode-   2.TZ second test mode-   3.TZ third test mode-   A2 a_a first exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE2 a) for    the first sub-signal (S2 a) of the second analogue signal (S2)-   A2 a_b second exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE2 a) for    the first sub-signal (S2 a) of the second analogue signal (S2)-   A2 b_a first exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE2 b) for    the second sub-signal (S2 b) of the second analogue signal (S2)-   A2 b_b second exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE2 b) for    the second sub-signal (S2 b) of the second analogue signal (S2)-   A2 c_a first exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE2 c) for    the first sub-signal (S2 c) of the second analogue signal (S2)-   A2 c_b second exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE2 c) for    the third sub-signal (S2 c) of the second analogue signal (S2)-   A2 c_a′ first exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE2 c) for    the third sub-signal (S2 c) of the second analogue signal (S2), here    in an alternative exemplary embodiment-   A2 c_b′ second exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE2 c) for    the third sub-signal (S2 c) of the second analogue signal (S2), here    in an alternative exemplary embodiment-   A3 a_a first exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE3 a) for    the first sub-signal (S3 a) of the third analogue signal (S3)-   A3 a_b second exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE3 a) for    the first sub-signal (S3 a) of the third analogue signal (S3)-   A3 b_a first exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE3 b) for    the second sub-signal (S3 b) of the third analogue signal (S3)-   A3 b_b second exemplary analysis signal for the coefficient    monitoring in the coefficient monitoring sub-apparatus (KUE3 b) for    the second sub-signal (S3 b) of the third analogue signal (S3)-   A_a first internal analysis signal of the coefficient monitoring    sub-apparatus (KUE) in question. It may be, for example, one of the    following signals with the following reference signs: A2 a_a, A2    b_a, A2 c_a, A3 a_a, A3 b_a. Other internal, symmetrical signals may    also be monitored. The first internal analysis signal must always be    selected to match the provided temporal symmetry of the signal to be    analysed (ZA) and with the same period duration T as the signal to    be analysed (ZA). If, for example, the first sub-signal (S2 a) of    the second analogue signal (S2) should be monitored, the first    internal analysis signal should not have pulses in each period T, as    shown in FIG. 51 for the third sub-signal (S2 c) of the second    analogue signal (S2) for the corresponding first analysis signal (A2    c_a), and instead should be in-phase only in each second period. The    first internal analysis signal is preferably generated digitally by    the digital signal generating unit (DSO).-   A_b second internal analysis signal of the coefficient monitoring    sub-apparatus (KUE) in question. It may be, for example, one of the    following signals with the following reference signs: A2 a_b, A2    b_b, A2 c_b, A3 a_b, A3 b_b. Other internal, symmetrical signals may    also be monitored. The second internal analysis signal must always    be selected to match the provided temporal symmetry of the signal to    be analysed (ZA) and with the same period duration T as the signal    to be analysed (ZA). If, for example, the first sub-signal (S2 a) of    the second analogue signal (S2) should be monitored, the second    internal analysis signal should not have pulses in each period T, as    shown in FIG. 51 for the third sub-signal (S2 c) of the second    analogue signal (S2) for the corresponding second analysis signal    (A2 c_b), and instead should be in-phase only in each second period.    The second internal analysis signal is preferably generated    digitally by the digital signal generating unit (DSO).-   ADC analogue-to-digital converter-   ACS analogue channel simulation unit-   AMX analogue multiplexer-   AP decay phase-   arctan angle calculation unit. Each coefficient monitoring    sub-apparatus (KUE) preferably has an angle calculation unit, of the    coefficient monitoring sub-apparatus (KUE) is realised in the for of    FIG. 52. The angle calculation unit generates the angle signal (sα)    from the first internal coefficient signal (s3 a) and the second    internal coefficient signal (s3 b). The angle signal preferably    represents the arctan or the arccot of the ratio of the level of the    first internal coefficient signal (s3 a) and of the second internal    coefficient signal (s3 b). Approximations and other evaluations (for    example simple division, etc.) are conceivable.-   AS analogue input circuit (has the function of an    analogue-to-digital converter (ADC))-   ASS outer region outside the measuring system (SS)-   AV analogue filter or analogue amplifier-   C_X internal comparator. Coefficient monitoring sub-apparatuses    (KUE) preferably have an internal comparator (C_X), if the    coefficient monitoring sub-apparatus (KUE) is realised in the form    of FIG. 52. In particular, in respect of FIG. 53, it may be formed    by the comparators with the reference signs C15, C16, C17, C18 and    C19, which are not shown in FIG. 53 for reasons of simplicity and    are situated within the corresponding coefficient monitoring    sub-apparatuses with the reference signs KUE2 a, KUE2 b, KUE2 c,    KUE3 a and KUE3 b. The internal comparator compares the level of the    angle signal (sα) with the internal reference value (Ref_X). The    internal reference value (Ref_X), in respect of FIG. 53, may be    formed in particular by reference values with the reference signs    Ref15, Ref16, Ref17, Ref18 and Ref19, which are not shown in FIG. 53    for reasons of simplicity and are situated within the corresponding    coefficient monitoring sub-apparatuses with the reference signs KUE2    a, KUE2 b, KUE2 c, KUE3 a and KUE3 b. Depending on the result of    this comparison, the internal comparator generates an internal    comparison result signal (v_X). The internal comparison result    signal (v_X), in respect of FIG. 53, may be formed in particular by    comparison result signals with the reference signs v15, v16, v17,    v18 and v19, which are formed within the corresponding coefficient    monitoring sub-apparatuses with the reference signs KUE2 a, KUE2 b,    KUE2 c, KUE3 a and KUE3 b. second internal comparator. In one    implementation, coefficient monitoring sub-apparatuses (KUE)    preferably have a second internal comparator (C_Y), if the    coefficient monitoring sub-apparatus (KUE) is realised in the form    of FIG. 54. In particular, in respect of FIG. 53, it may be formed    by the comparators which are not shown in FIG. 53 for reasons of    simplicity and are situated within the corresponding coefficient    monitoring sub-apparatuses with the reference signs KUE2 a, KUE2 b,    KUE2 c, KUE3 a and KUE3 b. The second internal comparator compares    the level of the first internal coefficient signal (s3 a) with the    second internal reference value (Ref_Y). The second internal    reference value (Ref_Y), in respect of FIG. 53, may be formed in    particular by reference values which are not shown in FIG. 53 for    reasons of simplicity and are situated within the corresponding    coefficient monitoring sub-apparatuses with the reference signs KUE2    a, KUE2 b, KUE2 c, KUE3 a and KUE3 b. Depending on the result of    this comparison, the second internal comparator generates a second    internal comparison result signal (v_Y). The second internal    comparison result signal (v_Y), in respect of FIG. 53, may be formed    in particular by comparison result signals which are formed within    the corresponding coefficient monitoring sub-apparatuses with the    reference signs KUE2 a, KUE2 b, KUE2 c, KUE3 a and KUE3 b and are    not shown in FIG. 53 for reasons of simplicity.-   C_Z third internal comparator. In one implementation, coefficient    monitoring sub-apparatuses (KUE) preferably have a third internal    comparator (C_Z), if the coefficient monitoring sub-apparatus (KUE)    is realised in the form of FIG. 54. In particular, in respect of    FIG. 53, it may be formed by the comparators which are not shown in    FIG. 53 for reasons of simplicity and are situated within the    corresponding coefficient monitoring sub-apparatuses with the    reference signs KUE2 a, KUE2 b, KUE2 c, KUE3 a and KUE3 b. The third    internal comparator compares the level of the second internal    coefficient signal (s1 b) with the third internal reference value    (Ref_Z). The third internal reference value (Ref_Z), in respect of    FIG. 53, may be formed in particular by reference values which are    not shown in FIG. 53 for reasons of simplicity and are situated    within the corresponding coefficient monitoring sub-apparatuses with    the reference signs KUE2 a, KUE2 b, KUE2 c, KUE3 a and KUE3 b.    Depending on the result of this comparison, the third internal    comparator generates a third internal comparison result signal    (v_Z). The third internal comparison result signal (v_Z), in respect    of FIG. 53, may be formed in particular by comparison result signals    which are formed within the corresponding coefficient monitoring    sub-apparatuses with the reference signs KUE2 a, KUE2 b, KUE2 c,    KUE3 a and KUE3 b and are not shown in FIG. 53 for reasons of    simplicity.-   C1 first comparator. The first comparator compares the first    difference signal (d1) with the first reference value (Ref1) and    generates the first comparison result signal (v1)-   C2 second comparator. The second comparator compares the first    sub-signal (S3 a) of the third analogue signal (S3) with the second    reference value (Ref2) and generates the second comparison result    signal (v2)-   C3 third comparator. The third comparator compares the second    sub-signal (S3 b) of the third analogue signal (S3) with the third    reference value (Ref3) and generates the third comparison result    signal (v3)-   C4 fourth comparator. The fourth comparator compares the second    sub-signal (S2 b) of the second analogue signal (S2) with the fourth    reference value (Ref4) and generates the fourth comparison result    signal (v4)-   C5 fifth comparator. The fifth comparator compares the third    sub-signal (S2 c) of the second analogue signal (S2) with the fifth    reference value (Ref5) and generates the fifth comparison result    signal (v5)-   C6 sixth comparator. The sixth comparator compares the first    sub-signal (S2 a) of the second analogue signal (S2) with the sixth    reference value (Ref6) and generates the sixth comparison result    signal (v6)-   C10 tenth comparator. The tenth comparator compares the second    difference signal (d2) with the seventh reference value (Ref7) and    generates the tenth comparison result signal (v10)-   C11 eleventh comparator. The eleventh comparator compares the third    difference signal (d3) with the eighth reference value (Ref8) and    generates the eleventh comparison result signal (v11)-   C12 twelfth comparator. The twelfth comparator compares the fourth    difference signal (d4) with the ninth reference value (Ref9) and    generates the twelfth comparison result signal (v12)-   C13 thirteenth comparator. The thirteenth comparator compares the    integrated fifth difference signal (d5 i) with the thirteenth    reference value (Ref13) and generates the thirteenth comparison    result signal (v13)-   C14 fourteenth comparator. The fourteenth comparator compares the    integrated fifth difference signal (d5 i) with the fourteenth    reference value (Ref14) and generates the fourteenth comparison    result signal (v14)-   C15 fifteenth comparator. The fifteenth comparator compares the    angle signal (sα) within the coefficient monitoring sub-apparatus    (KUE3 a) of the first sub-signal (S3 a) of the third analogue signal    (S3) with the fifteenth reference value (Ref15) and generates the    fifteenth comparison result signal (v15). The fifteenth comparator    (C15) is situated within the coefficient monitoring sub-apparatus    (KUE3 a) of the first sub-signal (S3 a) of the third analogue signal    (S3)-   C16 sixteenth comparator. The sixteenth comparator compares the    angle signal (sα) within the coefficient monitoring sub-apparatus    (KUE3 b) of the second sub-signal (S3 b) of the third analogue    signal (S3) with the sixteenth reference value (Ref16) and generates    the sixteenth comparison result signal (v16). The sixteenth    comparator (C16) is situated within the coefficient monitoring    sub-apparatus (KUE3 b) of the second sub-signal (S3 b) of the third    analogue signal (S3)-   C17 seventeenth comparator. The seventeenth comparator compares the    angle signal (sα) within the coefficient monitoring sub-apparatus    (KUE2 b) of the second sub-signal (S2 b) of the second analogue    signal (S2) with the seventeenth reference value (Ref17) and    generates the seventeenth comparison result signal (v17). The    seventeenth comparator (C17) is situated within the coefficient    monitoring sub-apparatus (KUE2 b) of the second sub-signal (S2 b) of    the second analogue signal (S2)-   C18 eighteenth comparator. The eighteenth comparator compares the    angle signal (sα) within the coefficient monitoring sub-apparatus    (KUE2 c) of the third sub-signal (S2 c) of the second analogue    signal (S2) with the eighteenth reference value (Ref18) and    generates the eighteenth comparison result signal (v18). The    eighteenth comparator (C18) is situated within the coefficient    monitoring sub-apparatus (KUE2 c) of the third sub-signal (S2 c) of    the second analogue signal (S2)-   C19 nineteenth comparator. The nineteenth comparator compares the    angle signal (sα) within the coefficient monitoring sub-apparatus    (KUE2 a) of the first sub-signal (S2 a) of the second analogue    signal (S2) with the nineteenth reference value (Ref19) and    generates the nineteenth comparison result signal (v19). The    nineteenth comparator (C19) is situated within the coefficient    monitoring sub-apparatus (KUE2 a) of the first sub-signal (S2 a) of    the second analogue signal (S2)-   CN measuring channel, in particular an ultrasound measuring channel-   CTR control device-   CT_(TR) transducer capacitor-   d1 first difference signal. The first difference signal in the    example of FIG. 3 represents the difference in the values of the    signal amplitudes (as exemplary parameter values) between the first    sub-signal (S3 a) of the third analogue signal (S3) and the second    sub-signal (S3 b) of the third analogue signal (S3).

d2 second difference signal. The second difference signal in the exampleof FIG. 5 represents the difference in the values of the signalamplitudes (as exemplary parameter values) between the second sub-signal(S2 b) of the second analogue signal (S2) and the third sub-signal (S2c) of the second analogue signal (S2).

-   d3 third difference signal. The third difference signal in the    example of FIG. 5 represents the difference in the values of the    signal amplitudes (as exemplary parameter values) between the third    sub-signal (S2 c) of the second analogue signal (S2) and the first    sub-signal (S2 a) of the second analogue signal (S2).-   d4 fourth difference signal. The fourth difference signal in the    example of FIG. 5 represents the difference in the values of the    signal amplitudes (as exemplary parameter values) between the first    sub-signal (S2 a) of the second analogue signal (S2) and the second    sub-signal (S2 b) of the second analogue signal (S2).-   d5 fifth difference signal. The fifth difference signal in the    example of FIG. 49 represents the difference in the values of the    signal amplitudes (as exemplary parameter values) between the first    sub-signal (S3 am) of the third buffered signal (S3 m) and the    second sub-signal (S3 bm) of the third buffered signal (S3 m).-   d5 i integrated fifth difference signal. The integrated fifth    difference signal in the example of FIG. 49 represents the output of    the second integrator (INT2), which integrates the fifth difference    signal (d5) over m clock periods T before it is preferably reset    again. Here, m is a positive integer. At the end of the m clock    periods the value of the integrated fifth difference signal    represents a measure for the asymmetry of the two sub-signals of the    third analogue signal (S3).-   d6 sixth difference signal. The sixth difference signal in the    example of FIG. 50 represents the difference in the values of the    signal amplitudes (as exemplary parameter values) between the first    sub-signal (S2 am) of the second buffered signal (S2 m) and the    second sub-signal (S2 bm) of the second buffered signal (S2 m).-   d6 i integrated sixth difference signal. The integrated sixth    difference signal in the example of FIG. 50 represents the output of    the first integrator (INT1), which integrates the sixth difference    signal (d6) over m clock periods T before it is preferably reset    again. At the end of the m clock periods the value of the integrated    sixth difference signal represents a measure for the asymmetry of    the two sub-signals of the second analogue signal (S3).-   D1 first difference amplifier. The first difference amplifier for    example forms the first difference signal (d1) by establishing a    difference from a parameter value of the first sub-signal (S3 a) of    the third analogue signal (S3) and from a parameter value of the    second sub-signal (S3 b) of the third analogue signal (S3).-   D2 second difference amplifier. The second difference amplifier for    example forms the second difference signal (d2) by establishing a    difference from a parameter value of the second sub-signal (S2 b) of    the second analogue signal (S2) and from a parameter value of the    third sub-signal (S2 c) of the second analogue signal (S2).-   D3 third difference amplifier. The third difference amplifier for    example forms the third difference signal (d3) by establishing a    difference from a parameter value of the third sub-signal (S2 c) of    the second analogue signal (S2) and from a parameter value of the    first sub-signal (S2 a) of the second analogue signal (S2).-   D4 fourth difference amplifier. The fourth difference amplifier for    example forms the fourth difference signal (d4) by establishing a    difference from a parameter value of the first sub-signal (S2 a) of    the second analogue signal (S2) and from a parameter value of the    second sub-signal (S2 b) of the second analogue signal (S2).-   D5 fifth difference amplifier. The fifth difference amplifier for    example forms the fifth difference signal (d5) by establishing a    difference from a parameter value of the first sub-signal (S3 am) of    the third buffered signal (S3 m) and from a parameter value of the    second sub-signal (S3 bm) of the third buffered signal (S3 m).-   D6 sixth difference amplifier. The sixth difference amplifier for    example forms the sixth difference signal (d6) by establishing a    difference from a parameter value of the first sub-signal (S2 am) of    the second buffered signal (S2 m) and from a parameter value of the    second sub-signal (S2 bm) of the second buffered signal (S2 m).-   DCS digital channel simulation unit-   DMX digital multiplexer-   DR driver stage-   DSI digital input circuit-   DSO digital signal generating unit-   EP receive phase-   ES receive signal, in particular an ultrasound receive signal-   EZ switched-on mode-   F1 first filter. Each coefficient monitoring sub-apparatus (KUE)    preferably comprises a first filter if the coefficient monitoring    sub-apparatus (KUE) is realised in the form of FIG. 52. The first    filter filters the first internal filter input signal (s1 a) to form    a first filter output signal (s2 a). The first filter is preferably    an integrator or at least a low-pass filter. The first filter with    the first multiplier (M1) thus forms a first scalar product unit and    thus together with the first multiplier (M1) forms a scalar product    from the signal to be analysed (ZA) and the first analysis signal    (A_a). The first filter output signal (s2 a) thus represents this    scalar product determined in this way. However, the limits of this    first scalar product are still unknown. The subsequent first    internal sample-and-hold unit (S&H_Ca) must therefore be    supplemented necessarily by the first scalar product unit.-   F2 second filter. Each coefficient monitoring sub-apparatus (KUE)    preferably comprises a second filter if the coefficient monitoring    sub-apparatus (KUE) is realised in the form of FIG. 52. The second    filter filters the second internal filter input signal (s1 b) to    form a second filter output signal (s2 b). The second filter is    preferably an integrator or at least a low-pass filter. The second    filter with the second multiplier (M2) thus forms a second scalar    product unit and thus together with the second multiplier (M2) forms    a scalar product from the signal to be analysed (ZA) and the second    analysis signal (A_b). The second filter output signal (s2 b) thus    represents this scalar product determined in this way. However, the    limits of this second scalar product are still unknown. The    subsequent second internal sample-and-hold unit (S&H_Cb) must    therefore be supplemented necessarily by the scalar product unit.-   FZ error mode-   INT1 first integrator-   INT2 second integrator-   IO data interface-   KUE coefficient monitoring sub-apparatus-   KUE2 a coefficient monitoring sub-apparatus of the first sub-signal    (S2 a) of the second analogue signal (S2)-   KUE2 b coefficient monitoring sub-apparatus of the second sub-signal    (S2 b) of the second analogue signal (S2)-   KUE3 a coefficient monitoring sub-apparatus of the first sub-signal    (S3 a) of the third analogue signal (S3)-   KUE3 b coefficient monitoring sub-apparatus of the second sub-signal    (S3 a) of the third analogue signal (S3)-   m number of clock periods over which the integration is performed-   M1 first multiplier. Each coefficient monitoring sub-apparatus (KUE)    preferably comprises a first multiplier if the coefficient    monitoring sub-apparatus (KUE) is realised in the form of FIG. 52.    The first multiplier, within the coefficient monitoring    sub-apparatus (KUE) in question, multiplies the first internal    analysis signal A_a relevant to the coefficient monitoring    sub-apparatus (KUE) in question by the signal to be analysed (ZA)    for the coefficient monitoring sub-apparatus (KUE) in question in    order to obtain a first internal filter input signal (s1 a).-   M2 second multiplier. Each coefficient monitoring sub-apparatus    (KUE) preferably comprises a second multiplier if the coefficient    monitoring sub-apparatus (KUE) is realised in the form of FIG. 52.    The second multiplier, within the coefficient monitoring    sub-apparatus (KUE) in question, multiplies the second internal    analysis signal A_b relevant to the coefficient monitoring    sub-apparatus (KUE) in question by the signal to be analysed (ZA)    for the coefficient monitoring sub-apparatus (KUE) in question in    order to obtain a second internal filter input signal (s1 b).-   MS measuring signal, in particular an ultrasound measuring signal-   Ref_X internal reference value. Coefficient monitoring    sub-apparatuses (KUE) preferably use an internal reference value if    they are realised in the form of FIG. 52. The internal reference    value (Ref_X), in respect of FIG. 53, may be formed in particular by    reference values with the reference signs Ref15, Ref16, Ref17, Ref18    and Ref19, which are not shown in FIG. 53 for reasons of    simplification and are arranged within the corresponding coefficient    monitoring sub-apparatuses with the reference signs KUE2 a, KUE2 b,    KUE2 c, KUE3 a and KUE3 b.-   Ref_Y second internal reference value. Coefficient monitoring    sub-apparatuses (KUE) preferably use a second internal reference    value (Ref_Y) if they are realised in the form of FIG. 54, 55 or 56.    The second internal reference value (Ref_Y), in respect of FIG. 53,    may be formed by reference values which are not shown in FIG. 53 for    reasons of simplification and are arranged within the corresponding    coefficient monitoring sub-apparatuses with the reference signs KUE2    a, KUE2 b, KUE2 c, KUE3 a and KUE3 b.-   Ref_Z third internal reference value. Coefficient monitoring    sub-apparatuses (KUE) preferably use a third internal reference    value (Ref_Z) if they are realised in the form of FIG. 54, 55 or 56.    The third internal reference value (Ref_Z), in respect of FIG. 53,    may be formed by reference values which are not shown in FIG. 53 for    reasons of simplification and are arranged within the corresponding    coefficient monitoring sub-apparatuses with the reference signs KUE2    a, KUE2 b, KUE2 c, KUE3 a and KUE3 b.-   Ref1 first reference value. The first reference value is used as a    comparison value for the first difference signal (d1) for generation    of the first comparison result signal (v1) by the first comparator    (C1).-   Ref2 second reference value. The second reference value is used as a    comparison value for the first sub-signal (S3 a) of the third    analogue signal (S3) for generation of the second comparison result    signal (v2) by the second comparator (C2).-   Ref3 third reference value. The third reference value is used as a    comparison value for the second sub-signal (S3 b) of the third    analogue signal (S3) for generation of the third comparison result    signal (v3) by the third comparator (C3).-   Ref4 fourth reference value. The fourth reference value is used as a    comparison value for the second sub-signal (S2 b) of the second    analogue signal (S2) for generation of the fourth comparison result    signal (v4) by the fourth comparator (C4).-   Ref5 fifth reference value. The fifth reference value is used as a    comparison value for the third sub-signal (S2 c) of the second    analogue signal (S2) for generation of the fifth comparison result    signal (v5) by the fifth comparator (C5).-   Ref6 sixth reference value. The sixth reference value is used as a    comparison value for the first sub-signal (S2 a) of the second    analogue signal (S2) for generation of the sixth comparison result    signal (v6) by the sixth comparator (C6).-   Ref7 seventh reference value. The seventh reference value is used as    a comparison value for the second difference signal (d2) for    generation of the tenth comparison result signal (v10) by the tenth    comparator (C10).-   Ref8 eighth reference value. The eighth reference value is used as a    comparison value for the third difference signal (d3) for generation    of the eleventh comparison result signal (v11) by the eleventh    comparator (C11).-   Ref9 ninth reference value. The ninth reference value is used as a    comparison value for the fourth difference signal (d4) for    generation of the twelfth comparison result signal (v12) by the    twelfth comparator (C12).-   Ref13 thirteenth reference value. The thirteenth reference value is    used as a comparison value for the integrated sixth difference    signal (d6 i) for generation of the thirteenth comparison result    signal (v13) by the thirteenth comparator (C13).-   Ref14 fourteenth reference value. The fourteenth reference value is    used as a comparison value for the integrated fifth difference    signal (d5 i) for generation of the fourteenth comparison result    signal (v14) by the fourteenth comparator (C14).-   Ref15 fifteenth reference value. The fifteenth reference value is    used as a comparison value for the angle signal (sα) within the    coefficient monitoring sub-apparatus (KUE3 a) of the first    sub-signal (S3 a) of the third analogue signal (S3) for generation    of the fifteenth comparison result signal (v15) by the fifteenth    comparator (C15) within the coefficient monitoring sub-apparatus    (KUE3 a) of the first sib-signal-   (S3 a) of the third analogue signal (S3).-   Ref16 sixteenth reference value. The sixteenth reference value is    used as a comparison value for the angle signal (sα) within the    coefficient monitoring sub-apparatus (KUE3 b) of the second    sub-signal (S3 b) of the third analogue signal (S3) for generation    of the sixteenth comparison result signal (v16) by the sixteenth    comparator (C16) within the coefficient monitoring sub-apparatus    (KUE3 b) of the second sub-signal (S3 b) of the third analogue    signal (S3).-   Ref17 seventeenth reference value. The seventeenth reference value    is used as a comparison value for the angle signal (sα) within the    coefficient monitoring sub-apparatus (KUE2 b) of the second    sub-signal (S2 b) of the second analogue signal (S2) for generation    of the seventeenth comparison result signal (v17) by the seventeenth    comparator (C17) within the coefficient monitoring sub-apparatus    (KUE2 b) of the second sub-signal (S2 b) of the second analogue    signal (S2).-   Ref18 eighteenth reference value. The eighteenth reference value is    used as a comparison value for the angle signal (sα) within the    coefficient monitoring sub-apparatus (KUE2 c) of the third    sub-signal (S2 c) of the second analogue signal (S2) for generation    of the eighteenth comparison result signal (v18) by the eighteenth    comparator (C18) within the coefficient monitoring sub-apparatus    (KUE2 c) of the third sub-signal (S2 c) of the second analogue    signal (S2).-   Ref19 nineteenth reference value. The nineteenth reference value is    used as a comparison value for the angle signal (sα) within the    coefficient monitoring sub-apparatus (KUE2 a) of the first    sub-signal (S2 a) of the second analogue signal (S2) for generation    of the nineteenth comparison result signal (v19) by the nineteenth    comparator (C19) within the coefficient monitoring sub-apparatus    (KUE2 a) of the first sub-signal (S2 a) of the second analogue    signal (S2).-   R_(TR) transducer resistor-   sα angle signal. Each coefficient monitoring sub-apparatus (KUE)    preferably comprises a signal angle if the coefficient monitoring    sub-apparatus (LUE) is realised in the form of FIG. 52. The angle    signal is generated by the angle calculation unit of the coefficient    monitoring sub-apparatus (LUE). The angle signal preferably    represents the arctan or the arccot of the ratio of the level of the    first internal coefficient signal (s3 a) and of the second internal    coefficient signal (s3 b). Approximations and other assessments (for    example simple division, etc.) are conceivable.-   S&H_Aa first phase shifter of the first symmetry checking apparatus    (SPA)-   S&H_Ab second phase shifter of the first symmetry checking apparatus    (SPA)-   S&H_Ba first phase shifter of the second symmetry checking apparatus    (SPB)-   S&H_Bb second phase shifter of the second symmetry checking    apparatus (SPB)-   S&H_Ca first internal sample-and-hold unit. Each coefficient    monitoring sub-apparatus (KUE) preferably comprises a first internal    sample-and-hold unit if the coefficient monitoring sub-apparatus    (KUE) is realised in the form of FIG. 52. The first internal    sample-and-hold unit samples the first internal filter output signal    (S2 a) at the temporal end of one or more complete periods T of the    signal to be analysed (ZA) and thus forms the first internal    coefficient signal (S3 a). The sampling occurs preferably only in    the transmission phase (SP) or at selected time periods within the    transmission phase (SP). The first internal sample-and-hold unit is    preferably controlled by the digital signal generating unit (DSO).-   S&H_Cb second internal sample-and-hold unit. Each coefficient    monitoring sub-apparatus (KUE) preferably comprises a second    internal sample-and-hold unit if the coefficient monitoring    sub-apparatus (KUE) is realised in the form of FIG. 52. The second    internal sample-and-hold unit samples the second internal filter    output signal (S2 b) at the temporal end of one or more complete    periods T of the signal to be analysed (ZA) and thus forms the    second internal coefficient signal (S3 b). The sampling occurs    preferably only in the transmission phase (SP) or at selected time    periods within the transmission phase (SP). The first internal    sample-and-hold unit is preferably controlled by the digital signal    generating unit (DSO).-   S0 control signal-   S1 first digital signal-   s1 a first internal filter input signal. Each coefficient monitoring    sub-apparatus (KUE) preferably comprises a first internal filter    input signal if the coefficient monitoring sub-apparatus (KUE) is    realised in the form of FIG. 52. The first filter input signal is    generated in the example of FIG. 52 by multiplying the signal to be    analysed (ZA) by the first internal analysis signal (A_a) by means    of the first multiplier (M1).-   s1 b second internal filter input signal. Each coefficient    monitoring sub-apparatus (KUE) preferably comprises a second    internal filter input signal if the coefficient monitoring    sub-apparatus (KUE) is realised in the form of FIG. 52. The second    filter input signal is generated in the example of FIG. 52 by    multiplying the signal to be analysed (ZA) by the second internal    analysis signal (A_a) by means of the second multiplier (M2).-   S2 second analogue signal-   s2 a first internal filter input signal. Each coefficient monitoring    sub-apparatus (KUE) preferably comprises a first internal filter    output signal if the coefficient monitoring sub-apparatus (KUE) is    realised in the form of FIG. 52. The first filter output signal is    generated in the example of FIG. 52 by filtering the first filter    input signal (sia) in the first internal filter (F1).-   S2 a first sub-signal of the second analogue signal (S2)-   S2 am first sub-signal of the second buffered signal (S2 m)-   s2 b second internal filter output signal. Each coefficient    monitoring sub-apparatus (KUE) preferably comprises a second    internal filter output signal if the coefficient monitoring    sub-apparatus (KUE) is realised in the form of FIG. 52. The second    filter output signal is generated in the example of FIG. 52 by    filtering the second filter input signal (s1 b) in the second    internal filter (F2).-   S2 b second sub-signal of the second analogue signal (S2)-   S2 bm second sub-signal of the buffered signal (S2 m)-   S2 c third sub-signal of the second analogue signal (S2)-   S2 cLC third sub-signal of the second analogue signal (S2) with    disconnection of the transducer capacitor (C_(TR)) (disrupted third    sub-signal of the second analogue signal (S2))-   S2 m second buffered signal-   S3 third analogue signal-   S3′ amplified third analogue signal-   s3 a third internal coefficient signal. Each coefficient monitoring    sub-apparatus (KUE) preferably comprises a first internal    coefficient signal if the coefficient monitoring sub-apparatus (KUE)    is realised in the form of FIG. 52. The first internal    sample-and-hold unit (S&H_Ca) forms the first internal coefficient    signal by sampling the first internal filter output signal (s2 a) at    the temporal end of one or more complete periods T of the signal to    be analysed (ZA). This sampling is performed preferably only in the    transmission phase (SP) or at selected time periods within the    transmission phase (SP). The sampling is preferably controlled by    the digital generating unit (DSO).-   s3 b second internal coefficient signal. Each coefficient monitoring    sub-apparatus (KUE) preferably comprises a second internal    coefficient signal if the coefficient monitoring sub-apparatus (KUE)    is realised in the form of FIG. 52. The second internal    sample-and-hold unit (S&H_Cb) forms the first internal coefficient    signal by sampling the second internal filter output signal (s2 b)    at the temporal end of one or more complete periods T of the signal    to be analysed (ZA). This sampling is performed preferably only in    the transmission phase (SP) or at selected time periods within the    transmission phase (SP). The sampling is preferably controlled by    the digital generating unit (DSO).-   S3 a first sub-signal of the third analogue signal (S3)-   S3 am first sub-signal of the third buffered signal (S3 m)-   S3 b second sub-signal of the third analogue signal (S3)-   S3 b m second sub-signal of the third buffered signal (S3 m)-   S3 m third buffered signal-   S3 t third analogue test signal-   S3 ta first sub-signal of the third analogue test signal-   S3 tb second sub-signal of the third analogue test signal-   S4 fourth analogue signal-   S5 fifth digital signal-   S5 t fifth digital test signal-   S6 sixth digital signal-   S7 seventh response signal-   SBA first symmetry checking apparatus-   SPB second symmetry checking apparatus-   SP transmission phase-   SS sensor system-   T clock period-   TR measuring unit, un particular an ultrasound transducer-   Tri inner ultrasound transducer-   UEB transmitter; v_X internal comparison signal. The coefficient    monitoring sub-apparatuses (LUE) preferably comprise an internal    comparison signal (v_X) if the coefficient monitoring    sub-apparatuses (KUE) are realised in the form of FIG. 52. In    particular, with respect to FIG. 53, the signals are comparison    signals with the reference signs v15, v16, v17, v18 and v19, which    for reasons of simplicity in FIG. 53 are not output signals of the    corresponding coefficient monitoring sub-apparatuses with the    reference signs KUE2 a, KUE2 b, KUE2 c, KUE3 a and KUE3 b. The    particular internal comparator (C_X) of the particular coefficient    monitoring sub-apparatus (KUE) compares the level of the angle    signal (sα) in question with the internal reference value (Ref_X) of    the corresponding coefficient monitoring sub-apparatus (KUE) (see    also FIG. 52). The internal reference value (Ref_X), with respect to    FIG. 53, may be formed by reference values with the reference signs    Ref15, Ref16, Ref17, Ref18 and Ref19, which for reasons of    simplicity are not shown in FIG. 53 and are situated within the    corresponding coefficient monitoring sub-apparatuses with the    reference signs KUE2 a, KUE2 b, KUE2 c, KUE3 a and KUE3 b. They thus    represent the internal reference value (Ref_X) of the particular    coefficient monitoring sub-apparatus KUE). Depending on the result    of this comparison, the internal comparator (C_X) generates the    internal comparison result signal (v_X). The internal comparison    result signal (v_X), with respect to FIG. 53, may be formed in    particular by comparison result signals with the reference signs    v15, v16, v17, v18 and v19 which are formed within the corresponding    coefficient monitoring sub-apparatuses with the reference signs KUE2    a, KUE2 b, KUE2 c, KUE3 a and KUE3 b. The control device (CTR)    and/or the digital input circuit (DSI) preferably assess the    internal comparison result signal (v_X) and generate an error    message as appropriate.-   v_Y second internal comparison signal. The coefficient monitoring    sub-apparatuses (LUE) preferably comprise a second internal    comparison signal (v_Y) if the coefficient monitoring    sub-apparatuses (KUE) are realised in the form of FIG. 54, 55 or 56.    In particular, with respect to FIG. 53, the signals are comparison    signals which for reasons of simplicity in FIG. 53 are not output    signals of the corresponding coefficient monitoring sub-apparatuses    with the reference signs KUE2 a, KUE2 b, KUE2 c, KUE3 a and KUE3 b.    The particular second internal comparator (C_Y) of the particular    coefficient monitoring sub-apparatus (KUE) compares the level of the    first internal coefficient signal (s3 a) with the second internal    reference value (Ref_Y) of the corresponding coefficient monitoring    sub-apparatus (KUE) (see also FIG. 54, 55 or 56). The second    internal reference value (Ref_Y), with respect to FIG. 53, may be    formed in particular by reference values which for reasons of    simplicity are not shown in FIG. 53 and may be situated within the    corresponding coefficient monitoring sub-apparatuses with the    reference signs KUE2 a, KUE2 b, KUE2 c, KUE3 a and KUE3 b. They thus    represent the second internal reference value (Ref_Y) of the    particular coefficient monitoring sub-apparatus (KUE). Depending on    the result of this comparison, the second internal comparator (C_Y)    generates the second internal comparison result signal (v_Y). The    second internal comparison result signals (v_Y), with respect to    FIG. 53, may be formed in particular by comparison result signals    which for reasons of simplicity are not shown in FIG. 53 and are    formed within the corresponding coefficient monitoring    sub-apparatuses with the reference signs KUE2 a, KUE2 b, KUE2 c,    KUE3 a and KUE3 b. The control device (CTR) and/or the digital input    circuit (DSI) preferably assess the second internal comparison    result signals (v_Y) and generate error messages as appropriate.-   v_Z third internal comparison signal. The coefficient monitoring    sub-apparatuses (KUE) preferably comprise a third internal    comparison signal (v_Z) if the coefficient monitoring    sub-apparatuses (KUE) are realised in the form of FIG. 54, 55 or 56.    In particular, with respect to FIG. 53, the signals may be    comparison signals which for reasons of simplicity in FIG. 53 are    not output signals of the corresponding coefficient monitoring    sub-apparatuses with the reference signs KUE2 a, KUE2 b, KUE2 c,    KUE3 a and KUE3 b. The particular third internal comparator (C_Z) of    the particular coefficient monitoring sub-apparatus (KUE) compares    the level of the second internal coefficient signal (s3 b) with the    third internal reference value (Ref_Z) of the corresponding    coefficient monitoring sub-apparatus (KUE) (see also FIG. 54, 55 or    56). The third internal reference value (Ref_Z), with respect to    FIG. 53, may be formed in particular by reference values which for    reasons of simplicity are not shown in FIG. 53 and may be situated    within the corresponding coefficient monitoring sub-apparatuses with    the reference signs KUE2 a, KUE2 b, KUE2 c, KUE3 a and KUE3 b. They    thus represent the third internal reference value (Ref_Z) of the    particular coefficient monitoring sub-apparatus (KUE). Depending on    the result of this comparison, the third internal comparator (C_Z)    generates the third internal comparison result signal (v_Z). The    third internal comparison result signals (v_Z), with respect to FIG.    53, may be formed in particular by comparison result signals which    for reasons of simplicity are not shown in FIG. 53 and are formed    within the corresponding coefficient monitoring sub-apparatuses with    the reference signs KUE2 a, KUE2 b, KUE2 c, KUE3 a and KUE3 b. The    control device (CTR) and/or the digital input circuit (DSI)    preferably assess the third internal comparison result signals (v_Z)    and generate error messages as appropriate.-   v1 first comparison result signal. In the example of FIG. 3 the    first comparison result signal represents the result of the    comparison between the value of the first difference signal (d1) and    the first reference value (Ref1). The comparison may be made without    or with consideration of the algebraic sign. A purely value-based    comparison is thus preferably a comparison of the absolute values.-   v2 second comparison result signal. In the example of FIG. 3 the    second comparison result signal represents the result of the    comparison between the value of the first sub-signal (S3 a) of the    third analogue signal (S3) and the second reference value (Ref2).    The comparison may be made without or with consideration of the    algebraic sign. A purely value-based comparison is thus preferably a    comparison of the absolute values.-   v3 third comparison result signal. In the example of FIG. 3 the    third comparison result signal represents the result of the    comparison between the value of the second sub-signal (S3 b) of the    third analogue signal (S3) and the second reference value (Ref2).    The comparison may be made without or with consideration of the    algebraic sign. A purely value-based comparison is thus preferably a    comparison of the absolute values.-   v4 fourth comparison result signal. In the example of FIG. 4 the    fourth comparison result signal represents the result of the    comparison between the value of the second sub-signal (S2 b) of the    second analogue signal (S2) and the fourth reference value (Ref4).    The comparison may be made without or with consideration of the    algebraic sign. A purely value-based comparison is thus preferably a    comparison of the absolute values.-   v5 fifth comparison result signal. In the example of FIG. 4 the    fifth comparison result signal represents the result of the    comparison between the value of the third sub-signal (S2 c) of the    second analogue signal (S2) and the fifth reference value (Ref5).    The comparison may be made without or with consideration of the    algebraic sign. A purely value-based comparison is thus preferably a    comparison of the absolute values.-   v6 sixth comparison result signal. In the example of FIG. 4 the    sixth comparison result signal represents the result of the    comparison between the value of the first sub-signal (S2 a) of the    second analogue signal (S2) and the sixth reference value (Ref6).    The comparison may be made without or with consideration of the    algebraic sign. A purely value-based comparison is thus preferably a    comparison of the absolute values.-   v10 tenth comparison result signal. In the example of FIG. 8 the    tenth comparison result signal represents the result of the    comparison between the value of the second difference signal (d2)    and the seventh reference value (Ref7) by the tenth comparator    (C10). The comparison may be made without or with consideration of    the algebraic sign. A purely value-based comparison is thus    preferably a comparison of the absolute values.-   v11 eleventh comparison result signal. In the example of FIG. 8 the    eleventh comparison result signal represents the result of the    comparison between the value of the third difference signal (d3) and    the eighth reference value (Ref8) by the eleventh comparator (C11).    The comparison may be made without or with consideration of the    algebraic sign. A purely value-based comparison is thus preferably a    comparison of the absolute values.-   v12 twelfth comparison result signal. In the example of FIG. 8 the    twelfth comparison result signal represents the result of the    comparison between the value of the fourth difference signal (d4)    and the ninth reference value (Ref9) by the twelfth comparator    (C12). The comparison may be made without or with consideration of    the algebraic sign. A purely value-based comparison is thus    preferably a comparison of the absolute values.-   v13 thirteenth comparison result signal. In the example of FIG. 50    the thirteenth comparison result signal represents the result of the    comparison between the value of the integrated sixth difference    signal (d6 i) and the thirteenth reference value (Ref13) by the    thirteenth comparator (C13). The comparison may be made without or    with consideration of the algebraic sign. A purely value-based    comparison is thus preferably a comparison of the absolute values.-   v14 fourteenth comparison result signal. In the example of FIG. 49    the fourteenth comparison result signal represents the result of the    comparison between the value of the integrated fifth difference    signal (d5 i) and the fourteenth reference value (Ref14) by the    fourteenth comparator (C14). The comparison may be made without or    with consideration of the algebraic sign. A purely value-based    comparison is thus preferably a comparison of the absolute values.-   v15 fifteenth comparison result signal. In the example of FIG. 53    the fifteenth comparison result signal preferably represents the    result of the comparison between the determined angle (for example    arctan(α)) of the two coefficients of the first sub-signal (S3 a) of    the third analogue signal (S3) and the fifteenth reference value    (Ref15) by the fifteenth comparator (C15), which is preferably    situated within the coefficient monitoring sub-apparatus (KUE3 a)    for the first sub-signal (S3 a) of the third analogue signal (S3).    The comparison may be made without or with consideration of the    algebraic sign. A purely value-based comparison is thus preferably a    comparison of the absolute values.-   v16 sixteenth comparison result signal. In the example of FIG. 53    the sixteenth comparison result signal preferably represents the    result of the comparison between the determined angle (for example    arctan(α)) of the two coefficients of the second sub-signal (S3 b)    of the third analogue signal (S3) and the sixteenth reference value    (Ref16) by the sixteenth comparator (C16), which is preferably    situated within the coefficient monitoring sub-apparatus (KUE3 b)    for the second sub-signal (S3 b) of the third analogue signal (S3).    The comparison may be made without or with consideration of the    algebraic sign. A purely value-based comparison is thus preferably a    comparison of the absolute values.-   v17 seventeenth comparison result signal. In the example of FIG. 53    the seventeenth comparison result signal preferably represents the    result of the comparison between the determined angle (for example    arctan(α)) of the two coefficients of the first sub-signal (S2 a) of    the second analogue signal (S2) and the seventeenth reference value    (Ref17) by the seventeenth comparator (C17), which is preferably    situated within the coefficient monitoring sub-apparatus (KUE2 a)    for the first sub-signal (S2 a) of the second analogue signal (S2).    The comparison may be made without or with consideration of the    algebraic sign. A purely value-based comparison is thus preferably a    comparison of the absolute values.-   v18 eighteenth comparison result signal. In the example of FIG. 53    the eighteenth comparison result signal preferably represents the    result of the comparison between the determined angle (for example    arctan(α)) of the two coefficients of the second sub-signal (S2 b)    of the second analogue signal (S2) and the eighteenth reference    value (Ref18) by the eighteenth comparator (C18), which is    preferably situated within the coefficient monitoring sub-apparatus    (KUE2 b) for the second sub-signal (S2 b) of the second analogue    signal (S2). The comparison may be made without or with    consideration of the algebraic sign. A purely value-based comparison    is thus preferably a comparison of the absolute values.-   v19 nineteenth comparison result signal. In the example of FIG. 53    the nineteenth comparison result signal preferably represents the    result of the comparison between the determined angle (for example    arctan(α)) of the two coefficients of the third sub-signal (S2 c) of    the second analogue signal (S2) and the nineteenth reference value    (Ref19) by the nineteenth comparator (C19), which is preferably    situated within the coefficient monitoring sub-apparatus (KUE2 c)    for the third sub-signal (S2 c) of the second analogue signal (S2).    The comparison may be made without or with consideration of the    algebraic sign. A purely value-based comparison is thus preferably a    comparison of the absolute values.-   Z1 first moment in time-   Z2 second moment in time-   z1 first moment in time for the storage of the determined    coefficients-   z2 second moment in time for the storage of the determined    coefficients-   z3 third moment in time for the storage of the determined    coefficients-   z4 fourth moment in time for the storage of the determined    coefficients-   ZA signal to be analysed by the coefficient monitoring sub-apparatus    (KUE) in question. This may be, for example, one of the following    signals with the following reference signs: S2 a, S2 b, S2 c, S3 a,    S3 b. Other internal, symmetrical signals may thus also be    monitored.-   zn n-th moment in time for the storage of the determined    coefficients

1. A self-testing measuring system (SS) comprising a digital signalgenerating unit (DSO), a driver stage (DR), a measuring unit (TR), whichtransmits an analogue output signal (MS) as measuring signal andreceives a receive signal (ES) in response thereto, an analogue inputcircuit (AS), a digital input circuit (DSI), an analogue channelsimulation unit (ACS), a digital channel simulation unit (DCS), ananalogue multiplexer (AMX), and a digital multiplexer (DMX), wherein themeasuring system (SS) may assume in an operating phase an operating modeand in a test phase, besides a first test mode, also a second test modeand/or a third test mode, and wherein in the operating mode the digitalsignal generating unit (DSO) generates a first digital signal (S1), thedriver stage (DR) converts this first digital signal (S1) of the digitalsignal generating unit (DSO) into a second analogue signal (S2), thissecond analogue signal (S2) prompts the measuring unit (TR) to transmitthe output signal (MS) as measurement signal into a measuring channel(CN), the measuring unit (TR) receives the receive signal (ES) from themeasuring channel (CN) depending on the output signal (MS), themeasuring unit (TR) generates a third analogue signal (S3) depending onthe received receive signal (ES), the analogue multiplexer (AMX)forwards this third analogue signal (S3) as fourth analogue signal (S4),the analogue input circuit (AS) converts the fourth analogue signal (S4)into a fifth digital signal (S5), the digital multiplexer (DMX) forwardsthe fifth digital signal (S5) as sixth digital signal (S6), the digitalinput circuit (DSI) receives the sixth digital signal (S6) and generatesa seventh response signal (S7), and the seventh response signal (S7) maybe used as measurement result or to form the measurement result, whereinin the first test mode the digital signal generating unit (DSO)generates a first digital signal (S1), the driver stage (DR) convertsthis first digital signal (S1) of the digital signal generating unit(DSO) into a second analogue signal (S2), this second analogue signal(S2) prompts the measuring unit (TR) to emit the output signal (MS) asmeasurement signal into a measuring channel (CN), the measuring unit(TR) receives the receive signal (ES) from the measuring channel (CN)depending on the output signal (MS), the measuring unit (TR) generates athird analogue signal (S3) depending on the received receive signal(ES), the analogue multiplexer (AMX) forwards this third analogue signal(S3) as fourth analogue signal (S4), the analogue input circuit (AS)converts the fourth analogue signal (S4) into a fifth digital signal(S5), the digital multiplexer (DMX) forwards the fifth digital signal assixth digital signal (S6), the digital input circuit (DSI) receives thesixth digital signal (S6) and generates a seventh response signal (S7),the seventh response signal (S7) may be used as test result or to formthe result of a check performed by the measuring system, wherein, in thesecond test mode, if provided, the digital signal generating unit (DSO)generates a first digital signal (S1), the driver stage (DR) convertsthis first digital signal (S1) of the digital signal generating unit(DSO) into a second analogue signal (S2), wherein the third analoguetest signal (S3 t) may also be a copy of the second analogue signal(S2), the analogue multiplexer (AMX) forwards this third analogue testsignal (S3 t) as fourth analogue signal (S4), the analogue input circuit(AS) converts the fourth analogue signal (S4) into a fifth digitalsignal (S5), the digital multiplexer (DMX) forwards the fifth digitalsignal (S5) as sixth digital signal (S6), the digital input circuit(DSI) receives the sixth digital signal (S6) and generates a seventhresponse signal (S7), and the seventh response signal (S7) may be usedas test result or to form the result of a check performed by themeasuring system, wherein, in the third test mode, if provided, thedigital signal generating unit (DSO) generates a first digital signal(S1), the digital channel simulation unit (DCS) converts this firstdigital signal (S1) into a fifth digital test signal (S5 t), wherein thefifth digital test signal (S5 t) may also be a copy of the first digitalsignal (S1), the digital multiplexer (DMX) forwards the fifth digitaltest signal (S5 t) as sixth digital signal (S6), the digital inputcircuit (DSI) receives the sixth digital signal (S6) and generates aseventh response signal (S7), and the seventh response signal (S7) maybe used as test result or to form the result of a check performed by themeasuring system. 2.-46. (canceled)